diff --git a/balancer_switching_test.go b/balancer_switching_test.go
index 0d8b2a545..e44198e66 100644
--- a/balancer_switching_test.go
+++ b/balancer_switching_test.go
@@ -40,7 +40,7 @@ func checkPickFirst(cc *ClientConn, servers []*server) error {
 	)
 	connected := false
 	for i := 0; i < 5000; i++ {
-		if err = Invoke(context.Background(), "/foo/bar", &req, &reply, cc); errorDesc(err) == servers[0].port {
+		if err = cc.Invoke(context.Background(), "/foo/bar", &req, &reply); errorDesc(err) == servers[0].port {
 			if connected {
 				// connected is set to false if peer is not server[0]. So if
 				// connected is true here, this is the second time we saw
@@ -58,7 +58,7 @@ func checkPickFirst(cc *ClientConn, servers []*server) error {
 	}
 	// The following RPCs should all succeed with the first server.
 	for i := 0; i < 3; i++ {
-		err = Invoke(context.Background(), "/foo/bar", &req, &reply, cc)
+		err = cc.Invoke(context.Background(), "/foo/bar", &req, &reply)
 		if errorDesc(err) != servers[0].port {
 			return fmt.Errorf("Index %d: want peer %v, got peer %v", i, servers[0].port, err)
 		}
@@ -80,7 +80,7 @@ func checkRoundRobin(cc *ClientConn, servers []*server) error {
 		for _, s := range servers {
 			var up bool
 			for i := 0; i < 5000; i++ {
-				if err = Invoke(context.Background(), "/foo/bar", &req, &reply, cc); errorDesc(err) == s.port {
+				if err = cc.Invoke(context.Background(), "/foo/bar", &req, &reply); errorDesc(err) == s.port {
 					up = true
 					break
 				}
@@ -94,7 +94,7 @@ func checkRoundRobin(cc *ClientConn, servers []*server) error {
 
 	serverCount := len(servers)
 	for i := 0; i < 3*serverCount; i++ {
-		err = Invoke(context.Background(), "/foo/bar", &req, &reply, cc)
+		err = cc.Invoke(context.Background(), "/foo/bar", &req, &reply)
 		if errorDesc(err) != servers[i%serverCount].port {
 			return fmt.Errorf("Index %d: want peer %v, got peer %v", i, servers[i%serverCount].port, err)
 		}
diff --git a/balancer_test.go b/balancer_test.go
index 3e0fa19be..d60fc3231 100644
--- a/balancer_test.go
+++ b/balancer_test.go
@@ -130,7 +130,7 @@ func TestNameDiscovery(t *testing.T) {
 	defer cc.Close()
 	req := "port"
 	var reply string
-	if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err == nil || errorDesc(err) != servers[0].port {
+	if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err == nil || errorDesc(err) != servers[0].port {
 		t.Fatalf("grpc.Invoke(_, _, _, _, _) = %v, want %s", err, servers[0].port)
 	}
 	// Inject the name resolution change to remove servers[0] and add servers[1].
@@ -146,7 +146,7 @@ func TestNameDiscovery(t *testing.T) {
 	r.w.inject(updates)
 	// Loop until the rpcs in flight talks to servers[1].
 	for {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[1].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[1].port {
 			break
 		}
 		time.Sleep(10 * time.Millisecond)
@@ -163,7 +163,7 @@ func TestEmptyAddrs(t *testing.T) {
 	}
 	defer cc.Close()
 	var reply string
-	if err := Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, cc); err != nil || reply != expectedResponse {
+	if err := cc.Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply); err != nil || reply != expectedResponse {
 		t.Fatalf("grpc.Invoke(_, _, _, _, _) = %v, reply = %q, want %q, <nil>", err, reply, expectedResponse)
 	}
 	// Inject name resolution change to remove the server so that there is no address
@@ -177,7 +177,7 @@ func TestEmptyAddrs(t *testing.T) {
 	for {
 		time.Sleep(10 * time.Millisecond)
 		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Millisecond)
-		if err := Invoke(ctx, "/foo/bar", &expectedRequest, &reply, cc); err != nil {
+		if err := cc.Invoke(ctx, "/foo/bar", &expectedRequest, &reply); err != nil {
 			cancel()
 			break
 		}
@@ -206,7 +206,7 @@ func TestRoundRobin(t *testing.T) {
 	var reply string
 	// Loop until servers[1] is up
 	for {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[1].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[1].port {
 			break
 		}
 		time.Sleep(10 * time.Millisecond)
@@ -219,14 +219,14 @@ func TestRoundRobin(t *testing.T) {
 	r.w.inject([]*naming.Update{u})
 	// Loop until both servers[2] are up.
 	for {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[2].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[2].port {
 			break
 		}
 		time.Sleep(10 * time.Millisecond)
 	}
 	// Check the incoming RPCs served in a round-robin manner.
 	for i := 0; i < 10; i++ {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err == nil || errorDesc(err) != servers[i%numServers].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err == nil || errorDesc(err) != servers[i%numServers].port {
 			t.Fatalf("Index %d: Invoke(_, _, _, _, _) = %v, want %s", i, err, servers[i%numServers].port)
 		}
 	}
@@ -242,7 +242,7 @@ func TestCloseWithPendingRPC(t *testing.T) {
 	}
 	defer cc.Close()
 	var reply string
-	if err := Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, cc, FailFast(false)); err != nil {
+	if err := cc.Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, FailFast(false)); err != nil {
 		t.Fatalf("grpc.Invoke(_, _, _, _, _) = %v, want %s", err, servers[0].port)
 	}
 	// Remove the server.
@@ -254,7 +254,7 @@ func TestCloseWithPendingRPC(t *testing.T) {
 	// Loop until the above update applies.
 	for {
 		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Millisecond)
-		if err := Invoke(ctx, "/foo/bar", &expectedRequest, &reply, cc, FailFast(false)); status.Code(err) == codes.DeadlineExceeded {
+		if err := cc.Invoke(ctx, "/foo/bar", &expectedRequest, &reply, FailFast(false)); status.Code(err) == codes.DeadlineExceeded {
 			cancel()
 			break
 		}
@@ -267,7 +267,7 @@ func TestCloseWithPendingRPC(t *testing.T) {
 	go func() {
 		defer wg.Done()
 		var reply string
-		if err := Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, cc, FailFast(false)); err == nil {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, FailFast(false)); err == nil {
 			t.Errorf("grpc.Invoke(_, _, _, _, _) = %v, want not nil", err)
 		}
 	}()
@@ -275,7 +275,7 @@ func TestCloseWithPendingRPC(t *testing.T) {
 		defer wg.Done()
 		var reply string
 		time.Sleep(5 * time.Millisecond)
-		if err := Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, cc, FailFast(false)); err == nil {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, FailFast(false)); err == nil {
 			t.Errorf("grpc.Invoke(_, _, _, _, _) = %v, want not nil", err)
 		}
 	}()
@@ -302,7 +302,7 @@ func TestGetOnWaitChannel(t *testing.T) {
 	for {
 		var reply string
 		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Millisecond)
-		if err := Invoke(ctx, "/foo/bar", &expectedRequest, &reply, cc, FailFast(false)); status.Code(err) == codes.DeadlineExceeded {
+		if err := cc.Invoke(ctx, "/foo/bar", &expectedRequest, &reply, FailFast(false)); status.Code(err) == codes.DeadlineExceeded {
 			cancel()
 			break
 		}
@@ -314,7 +314,7 @@ func TestGetOnWaitChannel(t *testing.T) {
 	go func() {
 		defer wg.Done()
 		var reply string
-		if err := Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, cc, FailFast(false)); err != nil {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, FailFast(false)); err != nil {
 			t.Errorf("grpc.Invoke(_, _, _, _, _) = %v, want <nil>", err)
 		}
 	}()
@@ -350,7 +350,7 @@ func TestOneServerDown(t *testing.T) {
 	var reply string
 	// Loop until servers[1] is up
 	for {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[1].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[1].port {
 			break
 		}
 		time.Sleep(10 * time.Millisecond)
@@ -374,7 +374,7 @@ func TestOneServerDown(t *testing.T) {
 			time.Sleep(sleepDuration)
 			// After sleepDuration, invoke RPC.
 			// server[0] is killed around the same time to make it racy between balancer and gRPC internals.
-			Invoke(context.Background(), "/foo/bar", &req, &reply, cc, FailFast(false))
+			cc.Invoke(context.Background(), "/foo/bar", &req, &reply, FailFast(false))
 			wg.Done()
 		}()
 	}
@@ -403,7 +403,7 @@ func TestOneAddressRemoval(t *testing.T) {
 	var reply string
 	// Loop until servers[1] is up
 	for {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[1].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[1].port {
 			break
 		}
 		time.Sleep(10 * time.Millisecond)
@@ -433,7 +433,7 @@ func TestOneAddressRemoval(t *testing.T) {
 			time.Sleep(sleepDuration)
 			// After sleepDuration, invoke RPC.
 			// server[0] is removed around the same time to make it racy between balancer and gRPC internals.
-			if err := Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, cc, FailFast(false)); err != nil {
+			if err := cc.Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, FailFast(false)); err != nil {
 				t.Errorf("grpc.Invoke(_, _, _, _, _) = %v, want not nil", err)
 			}
 			wg.Done()
@@ -452,7 +452,7 @@ func checkServerUp(t *testing.T, currentServer *server) {
 	defer cc.Close()
 	var reply string
 	for {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == port {
 			break
 		}
 		time.Sleep(10 * time.Millisecond)
@@ -469,7 +469,7 @@ func TestPickFirstEmptyAddrs(t *testing.T) {
 	}
 	defer cc.Close()
 	var reply string
-	if err := Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, cc); err != nil || reply != expectedResponse {
+	if err := cc.Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply); err != nil || reply != expectedResponse {
 		t.Fatalf("grpc.Invoke(_, _, _, _, _) = %v, reply = %q, want %q, <nil>", err, reply, expectedResponse)
 	}
 	// Inject name resolution change to remove the server so that there is no address
@@ -483,7 +483,7 @@ func TestPickFirstEmptyAddrs(t *testing.T) {
 	for {
 		time.Sleep(10 * time.Millisecond)
 		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Millisecond)
-		if err := Invoke(ctx, "/foo/bar", &expectedRequest, &reply, cc); err != nil {
+		if err := cc.Invoke(ctx, "/foo/bar", &expectedRequest, &reply); err != nil {
 			cancel()
 			break
 		}
@@ -501,7 +501,7 @@ func TestPickFirstCloseWithPendingRPC(t *testing.T) {
 	}
 	defer cc.Close()
 	var reply string
-	if err := Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, cc, FailFast(false)); err != nil {
+	if err := cc.Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, FailFast(false)); err != nil {
 		t.Fatalf("grpc.Invoke(_, _, _, _, _) = %v, want %s", err, servers[0].port)
 	}
 	// Remove the server.
@@ -513,7 +513,7 @@ func TestPickFirstCloseWithPendingRPC(t *testing.T) {
 	// Loop until the above update applies.
 	for {
 		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Millisecond)
-		if err := Invoke(ctx, "/foo/bar", &expectedRequest, &reply, cc, FailFast(false)); status.Code(err) == codes.DeadlineExceeded {
+		if err := cc.Invoke(ctx, "/foo/bar", &expectedRequest, &reply, FailFast(false)); status.Code(err) == codes.DeadlineExceeded {
 			cancel()
 			break
 		}
@@ -526,7 +526,7 @@ func TestPickFirstCloseWithPendingRPC(t *testing.T) {
 	go func() {
 		defer wg.Done()
 		var reply string
-		if err := Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, cc, FailFast(false)); err == nil {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, FailFast(false)); err == nil {
 			t.Errorf("grpc.Invoke(_, _, _, _, _) = %v, want not nil", err)
 		}
 	}()
@@ -534,7 +534,7 @@ func TestPickFirstCloseWithPendingRPC(t *testing.T) {
 		defer wg.Done()
 		var reply string
 		time.Sleep(5 * time.Millisecond)
-		if err := Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, cc, FailFast(false)); err == nil {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, FailFast(false)); err == nil {
 			t.Errorf("grpc.Invoke(_, _, _, _, _) = %v, want not nil", err)
 		}
 	}()
@@ -576,7 +576,7 @@ func TestPickFirstOrderAllServerUp(t *testing.T) {
 	req := "port"
 	var reply string
 	for i := 0; i < 20; i++ {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err == nil || errorDesc(err) != servers[0].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err == nil || errorDesc(err) != servers[0].port {
 			t.Fatalf("Index %d: Invoke(_, _, _, _, _) = %v, want %s", 0, err, servers[0].port)
 		}
 		time.Sleep(10 * time.Millisecond)
@@ -591,13 +591,13 @@ func TestPickFirstOrderAllServerUp(t *testing.T) {
 	r.w.inject([]*naming.Update{u})
 	// Loop until it changes to server[1]
 	for {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[1].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[1].port {
 			break
 		}
 		time.Sleep(10 * time.Millisecond)
 	}
 	for i := 0; i < 20; i++ {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err == nil || errorDesc(err) != servers[1].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err == nil || errorDesc(err) != servers[1].port {
 			t.Fatalf("Index %d: Invoke(_, _, _, _, _) = %v, want %s", 1, err, servers[1].port)
 		}
 		time.Sleep(10 * time.Millisecond)
@@ -611,7 +611,7 @@ func TestPickFirstOrderAllServerUp(t *testing.T) {
 	}
 	r.w.inject([]*naming.Update{u})
 	for i := 0; i < 20; i++ {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err == nil || errorDesc(err) != servers[1].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err == nil || errorDesc(err) != servers[1].port {
 			t.Fatalf("Index %d: Invoke(_, _, _, _, _) = %v, want %s", 1, err, servers[1].port)
 		}
 		time.Sleep(10 * time.Millisecond)
@@ -624,13 +624,13 @@ func TestPickFirstOrderAllServerUp(t *testing.T) {
 	}
 	r.w.inject([]*naming.Update{u})
 	for {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[2].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[2].port {
 			break
 		}
 		time.Sleep(1 * time.Second)
 	}
 	for i := 0; i < 20; i++ {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err == nil || errorDesc(err) != servers[2].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err == nil || errorDesc(err) != servers[2].port {
 			t.Fatalf("Index %d: Invoke(_, _, _, _, _) = %v, want %s", 2, err, servers[2].port)
 		}
 		time.Sleep(10 * time.Millisecond)
@@ -643,13 +643,13 @@ func TestPickFirstOrderAllServerUp(t *testing.T) {
 	}
 	r.w.inject([]*naming.Update{u})
 	for {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[0].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[0].port {
 			break
 		}
 		time.Sleep(1 * time.Second)
 	}
 	for i := 0; i < 20; i++ {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err == nil || errorDesc(err) != servers[0].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err == nil || errorDesc(err) != servers[0].port {
 			t.Fatalf("Index %d: Invoke(_, _, _, _, _) = %v, want %s", 0, err, servers[0].port)
 		}
 		time.Sleep(10 * time.Millisecond)
@@ -689,7 +689,7 @@ func TestPickFirstOrderOneServerDown(t *testing.T) {
 	req := "port"
 	var reply string
 	for i := 0; i < 20; i++ {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err == nil || errorDesc(err) != servers[0].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err == nil || errorDesc(err) != servers[0].port {
 			t.Fatalf("Index %d: Invoke(_, _, _, _, _) = %v, want %s", 0, err, servers[0].port)
 		}
 		time.Sleep(10 * time.Millisecond)
@@ -700,13 +700,13 @@ func TestPickFirstOrderOneServerDown(t *testing.T) {
 	servers[0].stop()
 	// Loop until it changes to server[1]
 	for {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[1].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[1].port {
 			break
 		}
 		time.Sleep(10 * time.Millisecond)
 	}
 	for i := 0; i < 20; i++ {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err == nil || errorDesc(err) != servers[1].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err == nil || errorDesc(err) != servers[1].port {
 			t.Fatalf("Index %d: Invoke(_, _, _, _, _) = %v, want %s", 1, err, servers[1].port)
 		}
 		time.Sleep(10 * time.Millisecond)
@@ -721,7 +721,7 @@ func TestPickFirstOrderOneServerDown(t *testing.T) {
 	checkServerUp(t, servers[0])
 
 	for i := 0; i < 20; i++ {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err == nil || errorDesc(err) != servers[1].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err == nil || errorDesc(err) != servers[1].port {
 			t.Fatalf("Index %d: Invoke(_, _, _, _, _) = %v, want %s", 1, err, servers[1].port)
 		}
 		time.Sleep(10 * time.Millisecond)
@@ -734,13 +734,13 @@ func TestPickFirstOrderOneServerDown(t *testing.T) {
 	}
 	r.w.inject([]*naming.Update{u})
 	for {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[0].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[0].port {
 			break
 		}
 		time.Sleep(1 * time.Second)
 	}
 	for i := 0; i < 20; i++ {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err == nil || errorDesc(err) != servers[0].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err == nil || errorDesc(err) != servers[0].port {
 			t.Fatalf("Index %d: Invoke(_, _, _, _, _) = %v, want %s", 0, err, servers[0].port)
 		}
 		time.Sleep(10 * time.Millisecond)
@@ -794,7 +794,7 @@ func TestPickFirstOneAddressRemoval(t *testing.T) {
 			time.Sleep(sleepDuration)
 			// After sleepDuration, invoke RPC.
 			// server[0] is removed around the same time to make it racy between balancer and gRPC internals.
-			if err := Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, cc, FailFast(false)); err != nil {
+			if err := cc.Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, FailFast(false)); err != nil {
 				t.Errorf("grpc.Invoke(_, _, _, _, _) = %v, want not nil", err)
 			}
 			wg.Done()
diff --git a/call_test.go b/call_test.go
index b95ade889..2bcea807f 100644
--- a/call_test.go
+++ b/call_test.go
@@ -217,7 +217,7 @@ func TestInvoke(t *testing.T) {
 	defer leakcheck.Check(t)
 	server, cc := setUp(t, 0, math.MaxUint32)
 	var reply string
-	if err := Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply, cc); err != nil || reply != expectedResponse {
+	if err := cc.Invoke(context.Background(), "/foo/bar", &expectedRequest, &reply); err != nil || reply != expectedResponse {
 		t.Fatalf("grpc.Invoke(_, _, _, _, _) = %v, want <nil>", err)
 	}
 	cc.Close()
@@ -229,7 +229,7 @@ func TestInvokeLargeErr(t *testing.T) {
 	server, cc := setUp(t, 0, math.MaxUint32)
 	var reply string
 	req := "hello"
-	err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc)
+	err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply)
 	if _, ok := status.FromError(err); !ok {
 		t.Fatalf("grpc.Invoke(_, _, _, _, _) receives non rpc error.")
 	}
@@ -246,7 +246,7 @@ func TestInvokeErrorSpecialChars(t *testing.T) {
 	server, cc := setUp(t, 0, math.MaxUint32)
 	var reply string
 	req := "weird error"
-	err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc)
+	err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply)
 	if _, ok := status.FromError(err); !ok {
 		t.Fatalf("grpc.Invoke(_, _, _, _, _) receives non rpc error.")
 	}
@@ -266,7 +266,7 @@ func TestInvokeCancel(t *testing.T) {
 	for i := 0; i < 100; i++ {
 		ctx, cancel := context.WithCancel(context.Background())
 		cancel()
-		Invoke(ctx, "/foo/bar", &req, &reply, cc)
+		cc.Invoke(ctx, "/foo/bar", &req, &reply)
 	}
 	if canceled != 0 {
 		t.Fatalf("received %d of 100 canceled requests", canceled)
@@ -285,7 +285,7 @@ func TestInvokeCancelClosedNonFailFast(t *testing.T) {
 	req := "hello"
 	ctx, cancel := context.WithCancel(context.Background())
 	cancel()
-	if err := Invoke(ctx, "/foo/bar", &req, &reply, cc, FailFast(false)); err == nil {
+	if err := cc.Invoke(ctx, "/foo/bar", &req, &reply, FailFast(false)); err == nil {
 		t.Fatalf("canceled invoke on closed connection should fail")
 	}
 	server.stop()
diff --git a/pickfirst_test.go b/pickfirst_test.go
index 2f85febff..9e1fd03df 100644
--- a/pickfirst_test.go
+++ b/pickfirst_test.go
@@ -58,14 +58,14 @@ func TestOneBackendPickfirst(t *testing.T) {
 	defer cancel()
 	req := "port"
 	var reply string
-	if err := Invoke(ctx, "/foo/bar", &req, &reply, cc); err == nil || status.Code(err) != codes.DeadlineExceeded {
+	if err := cc.Invoke(ctx, "/foo/bar", &req, &reply); err == nil || status.Code(err) != codes.DeadlineExceeded {
 		t.Fatalf("EmptyCall() = _, %v, want _, DeadlineExceeded", err)
 	}
 
 	r.NewAddress([]resolver.Address{{Addr: servers[0].addr}})
 	// The second RPC should succeed.
 	for i := 0; i < 1000; i++ {
-		if err = Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[0].port {
+		if err = cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[0].port {
 			return
 		}
 		time.Sleep(time.Millisecond)
@@ -92,14 +92,14 @@ func TestBackendsPickfirst(t *testing.T) {
 	defer cancel()
 	req := "port"
 	var reply string
-	if err := Invoke(ctx, "/foo/bar", &req, &reply, cc); err == nil || status.Code(err) != codes.DeadlineExceeded {
+	if err := cc.Invoke(ctx, "/foo/bar", &req, &reply); err == nil || status.Code(err) != codes.DeadlineExceeded {
 		t.Fatalf("EmptyCall() = _, %v, want _, DeadlineExceeded", err)
 	}
 
 	r.NewAddress([]resolver.Address{{Addr: servers[0].addr}, {Addr: servers[1].addr}})
 	// The second RPC should succeed with the first server.
 	for i := 0; i < 1000; i++ {
-		if err = Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[0].port {
+		if err = cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[0].port {
 			return
 		}
 		time.Sleep(time.Millisecond)
@@ -126,7 +126,7 @@ func TestNewAddressWhileBlockingPickfirst(t *testing.T) {
 	defer cancel()
 	req := "port"
 	var reply string
-	if err := Invoke(ctx, "/foo/bar", &req, &reply, cc); err == nil || status.Code(err) != codes.DeadlineExceeded {
+	if err := cc.Invoke(ctx, "/foo/bar", &req, &reply); err == nil || status.Code(err) != codes.DeadlineExceeded {
 		t.Fatalf("EmptyCall() = _, %v, want _, DeadlineExceeded", err)
 	}
 
@@ -136,7 +136,7 @@ func TestNewAddressWhileBlockingPickfirst(t *testing.T) {
 		go func() {
 			defer wg.Done()
 			// This RPC blocks until NewAddress is called.
-			Invoke(context.Background(), "/foo/bar", &req, &reply, cc)
+			cc.Invoke(context.Background(), "/foo/bar", &req, &reply)
 		}()
 	}
 	time.Sleep(50 * time.Millisecond)
@@ -163,7 +163,7 @@ func TestCloseWithPendingRPCPickfirst(t *testing.T) {
 	defer cancel()
 	req := "port"
 	var reply string
-	if err := Invoke(ctx, "/foo/bar", &req, &reply, cc); err == nil || status.Code(err) != codes.DeadlineExceeded {
+	if err := cc.Invoke(ctx, "/foo/bar", &req, &reply); err == nil || status.Code(err) != codes.DeadlineExceeded {
 		t.Fatalf("EmptyCall() = _, %v, want _, DeadlineExceeded", err)
 	}
 
@@ -173,7 +173,7 @@ func TestCloseWithPendingRPCPickfirst(t *testing.T) {
 		go func() {
 			defer wg.Done()
 			// This RPC blocks until NewAddress is called.
-			Invoke(context.Background(), "/foo/bar", &req, &reply, cc)
+			cc.Invoke(context.Background(), "/foo/bar", &req, &reply)
 		}()
 	}
 	time.Sleep(50 * time.Millisecond)
@@ -200,14 +200,14 @@ func TestOneServerDownPickfirst(t *testing.T) {
 	defer cancel()
 	req := "port"
 	var reply string
-	if err := Invoke(ctx, "/foo/bar", &req, &reply, cc); err == nil || status.Code(err) != codes.DeadlineExceeded {
+	if err := cc.Invoke(ctx, "/foo/bar", &req, &reply); err == nil || status.Code(err) != codes.DeadlineExceeded {
 		t.Fatalf("EmptyCall() = _, %v, want _, DeadlineExceeded", err)
 	}
 
 	r.NewAddress([]resolver.Address{{Addr: servers[0].addr}, {Addr: servers[1].addr}})
 	// The second RPC should succeed with the first server.
 	for i := 0; i < 1000; i++ {
-		if err = Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[0].port {
+		if err = cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[0].port {
 			break
 		}
 		time.Sleep(time.Millisecond)
@@ -215,7 +215,7 @@ func TestOneServerDownPickfirst(t *testing.T) {
 
 	servers[0].stop()
 	for i := 0; i < 1000; i++ {
-		if err = Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[1].port {
+		if err = cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[1].port {
 			return
 		}
 		time.Sleep(time.Millisecond)
@@ -242,14 +242,14 @@ func TestAllServersDownPickfirst(t *testing.T) {
 	defer cancel()
 	req := "port"
 	var reply string
-	if err := Invoke(ctx, "/foo/bar", &req, &reply, cc); err == nil || status.Code(err) != codes.DeadlineExceeded {
+	if err := cc.Invoke(ctx, "/foo/bar", &req, &reply); err == nil || status.Code(err) != codes.DeadlineExceeded {
 		t.Fatalf("EmptyCall() = _, %v, want _, DeadlineExceeded", err)
 	}
 
 	r.NewAddress([]resolver.Address{{Addr: servers[0].addr}, {Addr: servers[1].addr}})
 	// The second RPC should succeed with the first server.
 	for i := 0; i < 1000; i++ {
-		if err = Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[0].port {
+		if err = cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[0].port {
 			break
 		}
 		time.Sleep(time.Millisecond)
@@ -259,7 +259,7 @@ func TestAllServersDownPickfirst(t *testing.T) {
 		servers[i].stop()
 	}
 	for i := 0; i < 1000; i++ {
-		if err = Invoke(context.Background(), "/foo/bar", &req, &reply, cc); status.Code(err) == codes.Unavailable {
+		if err = cc.Invoke(context.Background(), "/foo/bar", &req, &reply); status.Code(err) == codes.Unavailable {
 			return
 		}
 		time.Sleep(time.Millisecond)
@@ -286,19 +286,19 @@ func TestAddressesRemovedPickfirst(t *testing.T) {
 	defer cancel()
 	req := "port"
 	var reply string
-	if err := Invoke(ctx, "/foo/bar", &req, &reply, cc); err == nil || status.Code(err) != codes.DeadlineExceeded {
+	if err := cc.Invoke(ctx, "/foo/bar", &req, &reply); err == nil || status.Code(err) != codes.DeadlineExceeded {
 		t.Fatalf("EmptyCall() = _, %v, want _, DeadlineExceeded", err)
 	}
 
 	r.NewAddress([]resolver.Address{{Addr: servers[0].addr}, {Addr: servers[1].addr}, {Addr: servers[2].addr}})
 	for i := 0; i < 1000; i++ {
-		if err = Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[0].port {
+		if err = cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[0].port {
 			break
 		}
 		time.Sleep(time.Millisecond)
 	}
 	for i := 0; i < 20; i++ {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err == nil || errorDesc(err) != servers[0].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err == nil || errorDesc(err) != servers[0].port {
 			t.Fatalf("Index %d: Invoke(_, _, _, _, _) = %v, want %s", 0, err, servers[0].port)
 		}
 		time.Sleep(10 * time.Millisecond)
@@ -307,13 +307,13 @@ func TestAddressesRemovedPickfirst(t *testing.T) {
 	// Remove server[0].
 	r.NewAddress([]resolver.Address{{Addr: servers[1].addr}, {Addr: servers[2].addr}})
 	for i := 0; i < 1000; i++ {
-		if err = Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[1].port {
+		if err = cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[1].port {
 			break
 		}
 		time.Sleep(time.Millisecond)
 	}
 	for i := 0; i < 20; i++ {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err == nil || errorDesc(err) != servers[1].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err == nil || errorDesc(err) != servers[1].port {
 			t.Fatalf("Index %d: Invoke(_, _, _, _, _) = %v, want %s", 1, err, servers[1].port)
 		}
 		time.Sleep(10 * time.Millisecond)
@@ -322,7 +322,7 @@ func TestAddressesRemovedPickfirst(t *testing.T) {
 	// Append server[0], nothing should change.
 	r.NewAddress([]resolver.Address{{Addr: servers[1].addr}, {Addr: servers[2].addr}, {Addr: servers[0].addr}})
 	for i := 0; i < 20; i++ {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err == nil || errorDesc(err) != servers[1].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err == nil || errorDesc(err) != servers[1].port {
 			t.Fatalf("Index %d: Invoke(_, _, _, _, _) = %v, want %s", 1, err, servers[1].port)
 		}
 		time.Sleep(10 * time.Millisecond)
@@ -331,13 +331,13 @@ func TestAddressesRemovedPickfirst(t *testing.T) {
 	// Remove server[1].
 	r.NewAddress([]resolver.Address{{Addr: servers[2].addr}, {Addr: servers[0].addr}})
 	for i := 0; i < 1000; i++ {
-		if err = Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[2].port {
+		if err = cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[2].port {
 			break
 		}
 		time.Sleep(time.Millisecond)
 	}
 	for i := 0; i < 20; i++ {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err == nil || errorDesc(err) != servers[2].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err == nil || errorDesc(err) != servers[2].port {
 			t.Fatalf("Index %d: Invoke(_, _, _, _, _) = %v, want %s", 2, err, servers[2].port)
 		}
 		time.Sleep(10 * time.Millisecond)
@@ -346,13 +346,13 @@ func TestAddressesRemovedPickfirst(t *testing.T) {
 	// Remove server[2].
 	r.NewAddress([]resolver.Address{{Addr: servers[0].addr}})
 	for i := 0; i < 1000; i++ {
-		if err = Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err != nil && errorDesc(err) == servers[0].port {
+		if err = cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err != nil && errorDesc(err) == servers[0].port {
 			break
 		}
 		time.Sleep(time.Millisecond)
 	}
 	for i := 0; i < 20; i++ {
-		if err := Invoke(context.Background(), "/foo/bar", &req, &reply, cc); err == nil || errorDesc(err) != servers[0].port {
+		if err := cc.Invoke(context.Background(), "/foo/bar", &req, &reply); err == nil || errorDesc(err) != servers[0].port {
 			t.Fatalf("Index %d: Invoke(_, _, _, _, _) = %v, want %s", 0, err, servers[0].port)
 		}
 		time.Sleep(10 * time.Millisecond)