diff --git a/build.gradle b/build.gradle
index f57c0add2..3d8345448 100644
--- a/build.gradle
+++ b/build.gradle
@@ -100,7 +100,7 @@ dependencies {
     testCompile group: 'com.googlecode.junit-toolbox', name: 'junit-toolbox', version: '2.4'
     testCompile group: 'ch.qos.logback', name: 'logback-classic', version: '1.2.3'
     testCompile group: 'io.grpc', name: 'grpc-testing', version: '1.54.2'
-    testImplementation 'io.opentracing:opentracing-mock:0.33.0'
+    testImplementation 'io.opentracing:opentracing-mock:0.32.0'
     testImplementation group: 'org.mockito', name: 'mockito-core', version: '4.5.1'
     testImplementation "org.mockito:mockito-inline:4.5.1" // for mocking final classes
 }
diff --git a/src/main/java/com/uber/cadence/serviceclient/ClientOptions.java b/src/main/java/com/uber/cadence/serviceclient/ClientOptions.java
index d7c7072d7..be311dc1c 100644
--- a/src/main/java/com/uber/cadence/serviceclient/ClientOptions.java
+++ b/src/main/java/com/uber/cadence/serviceclient/ClientOptions.java
@@ -26,6 +26,7 @@
 import io.grpc.ManagedChannel;
 import io.opentracing.Tracer;
 import io.opentracing.noop.NoopTracerFactory;
+import io.opentracing.util.GlobalTracer;
 import java.util.Map;
 
 public class ClientOptions {
@@ -130,7 +131,13 @@ private ClientOptions(Builder builder) {
     }
     this.authProvider = builder.authProvider;
     this.isolationGroup = builder.isolationGroup;
-    this.tracer = builder.tracer;
+    if (builder.tracer != null) {
+      this.tracer = builder.tracer;
+    } else {
+      // Default value is GlobalTracer. If the user overrides it with null, fall back to NoopTracer.
+      // We need some tracer instance
+      this.tracer = NoopTracerFactory.create();
+    }
   }
 
   public static ClientOptions defaultInstance() {
@@ -233,8 +240,8 @@ public static class Builder {
     private IAuthorizationProvider authProvider;
     private FeatureFlags featureFlags;
     private String isolationGroup;
-    // by default NoopTracer
-    private Tracer tracer = NoopTracerFactory.create();
+    // by default GlobalTracer
+    private Tracer tracer = GlobalTracer.get();
 
     private Builder() {}
 
diff --git a/src/main/java/com/uber/cadence/serviceclient/WorkflowServiceTChannel.java b/src/main/java/com/uber/cadence/serviceclient/WorkflowServiceTChannel.java
index d8d22695f..d2f08494c 100644
--- a/src/main/java/com/uber/cadence/serviceclient/WorkflowServiceTChannel.java
+++ b/src/main/java/com/uber/cadence/serviceclient/WorkflowServiceTChannel.java
@@ -86,7 +86,8 @@ public class WorkflowServiceTChannel implements IWorkflowService {
   public WorkflowServiceTChannel(ClientOptions options) {
     this.options = options;
     this.thriftHeaders = getThriftHeaders(options);
-    this.tChannel = new TChannel.Builder(options.getClientAppName()).build();
+    this.tChannel =
+        new TChannel.Builder(options.getClientAppName()).setTracer(options.getTracer()).build();
     this.tracingPropagator = new TracingPropagator(options.getTracer());
     this.tracer = options.getTracer();
 
diff --git a/src/test/java/com/uber/cadence/internal/sync/WorkflowClientInternalTest.java b/src/test/java/com/uber/cadence/internal/sync/WorkflowClientInternalTest.java
index 84facee0c..1956e5fbb 100644
--- a/src/test/java/com/uber/cadence/internal/sync/WorkflowClientInternalTest.java
+++ b/src/test/java/com/uber/cadence/internal/sync/WorkflowClientInternalTest.java
@@ -116,8 +116,18 @@ public void testEnqueueStart_includesTracing() {
     stub.enqueueStart("input");
 
     StartWorkflowExecutionAsyncRequest request = requestFuture.getNow(null).getStartRequest();
-    assertEquals(1, fakeService.getTracer().finishedSpans().size());
-    MockSpan mockSpan = fakeService.getTracer().finishedSpans().get(0);
+    MockSpan mockSpan =
+        fakeService
+            .getTracer()
+            .finishedSpans()
+            .stream()
+            .filter(span -> "cadence-StartWorkflowExecutionAsync".equals(span.operationName()))
+            .findFirst()
+            .orElseThrow(
+                () ->
+                    new AssertionError(
+                        "No span found for StartWorkflowExecutionAsync:"
+                            + fakeService.getTracer().finishedSpans()));
     assertEquals(
         mockSpan.context().toTraceId(),
         Charsets.UTF_8
@@ -269,8 +279,21 @@ public void testEnqueueSignalWithStart_includesTracing() {
 
     SignalWithStartWorkflowExecutionRequest request =
         requestFuture.getNow(null).getSignalWithStartRequest().getRequest();
-    assertEquals(1, fakeService.getTracer().finishedSpans().size());
-    MockSpan mockSpan = fakeService.getTracer().finishedSpans().get(0);
+    assertEquals(2, fakeService.getTracer().finishedSpans().size());
+    MockSpan mockSpan =
+        fakeService
+            .getTracer()
+            .finishedSpans()
+            .stream()
+            .filter(
+                span ->
+                    "cadence-SignalWithStartWorkflowExecutionAsync".equals(span.operationName()))
+            .findFirst()
+            .orElseThrow(
+                () ->
+                    new AssertionError(
+                        "No span found for SignalWithStartWorkflowExecutionAsync:"
+                            + fakeService.getTracer().finishedSpans()));
     assertEquals(
         mockSpan.context().toTraceId(),
         Charsets.UTF_8.decode(request.getHeader().getFields().get("traceid")).toString());
diff --git a/src/test/java/com/uber/cadence/internal/tracing/StartWorkflowTest.java b/src/test/java/com/uber/cadence/internal/tracing/StartWorkflowTest.java
index 23b39f000..357a35098 100644
--- a/src/test/java/com/uber/cadence/internal/tracing/StartWorkflowTest.java
+++ b/src/test/java/com/uber/cadence/internal/tracing/StartWorkflowTest.java
@@ -267,7 +267,8 @@ public void testSignalWithStartWorkflowGRPC() {
   public void testStartWorkflowTchannelNoPropagation() {
     Assume.assumeTrue(useDockerService);
     MockTracer mockTracer = new MockTracer();
-    IWorkflowService service = new WorkflowServiceTChannel(ClientOptions.newBuilder().build());
+    IWorkflowService service =
+        new WorkflowServiceTChannel(ClientOptions.newBuilder().setTracer(null).build());
     testStartWorkflowHelper(service, mockTracer, false);
   }
 
@@ -277,7 +278,8 @@ public void testStartWorkflowGRPCNoPropagation() {
     MockTracer mockTracer = new MockTracer();
     IWorkflowService service =
         new Thrift2ProtoAdapter(
-            IGrpcServiceStubs.newInstance(ClientOptions.newBuilder().setPort(7833).build()));
+            IGrpcServiceStubs.newInstance(
+                ClientOptions.newBuilder().setPort(7833).setTracer(null).build()));
     testStartWorkflowHelper(service, mockTracer, false);
   }
 
@@ -285,7 +287,8 @@ public void testStartWorkflowGRPCNoPropagation() {
   public void testSignalStartWorkflowTchannelNoPropagation() {
     Assume.assumeTrue(useDockerService);
     MockTracer mockTracer = new MockTracer();
-    IWorkflowService service = new WorkflowServiceTChannel(ClientOptions.newBuilder().build());
+    IWorkflowService service =
+        new WorkflowServiceTChannel(ClientOptions.newBuilder().setTracer(null).build());
     testSignalWithStartWorkflowHelper(service, mockTracer, false);
   }
 
@@ -295,7 +298,8 @@ public void testSignalStartWorkflowGRPCNoPropagation() {
     MockTracer mockTracer = new MockTracer();
     IWorkflowService service =
         new Thrift2ProtoAdapter(
-            IGrpcServiceStubs.newInstance(ClientOptions.newBuilder().setPort(7833).build()));
+            IGrpcServiceStubs.newInstance(
+                ClientOptions.newBuilder().setPort(7833).setTracer(null).build()));
     testSignalWithStartWorkflowHelper(service, mockTracer, false);
   }
 
@@ -330,7 +334,7 @@ private void testStartWorkflowHelper(
       int res = wf.AddOneThenDouble(3);
       assertEquals(8, res);
     } catch (Exception e) {
-      fail("workflow failure: " + e);
+      throw new AssertionError("workflow failure", e);
     } finally {
       rootSpan.finish();
       List<MockSpan> spans = mockTracer.finishedSpans();
@@ -358,19 +362,11 @@ private void testStartWorkflowHelper(
       } else {
         // assert start workflow
         MockSpan spanStartWorkflow =
-            spans
-                .stream()
-                .filter(span -> span.operationName().contains("StartWorkflow"))
-                .findFirst()
-                .orElse(null);
-        if (spanStartWorkflow == null) {
-          fail("StartWorkflow span not found");
-        }
+            getFirstSpanByOperationName(spans, "cadence-StartWorkflowExecution");
 
         // assert workflow spans
-        MockSpan spanExecuteWF = getLinkedSpans(spans, spanStartWorkflow.context()).get(0);
-        assertEquals(spanExecuteWF.operationName(), "cadence-ExecuteWorkflow");
-        assertSpanReferences(spanExecuteWF, "follows_from", spanStartWorkflow);
+        MockSpan spanExecuteWF = getFirstSpanByOperationName(spans, "cadence-ExecuteWorkflow");
+        assertChildOf(spans, spanExecuteWF, spanStartWorkflow);
 
         MockSpan spanExecuteActivity = getLinkedSpans(spans, spanExecuteWF.context()).get(0);
         assertEquals(spanExecuteActivity.operationName(), "cadence-ExecuteActivity");
@@ -432,7 +428,7 @@ private void testSignalWithStartWorkflowHelper(
       int res = wf.getResult(Integer.class);
       assertEquals(8, res);
     } catch (Exception e) {
-      fail("workflow failure: " + e);
+      throw new AssertionError("Workflow failure", e);
     } finally {
       rootSpan.finish();
       List<MockSpan> spans = mockTracer.finishedSpans();
@@ -460,21 +456,14 @@ private void testSignalWithStartWorkflowHelper(
       } else {
         // assert start workflow
         MockSpan spanStartWorkflow =
-            spans
-                .stream()
-                .filter(span -> span.operationName().contains("StartWorkflow"))
-                .findFirst()
-                .orElse(null);
-        if (spanStartWorkflow == null) {
-          fail("StartWorkflow span not found");
-        }
+            getFirstSpanByOperationName(spans, "cadence-SignalWithStartWorkflowExecution");
 
         // assert workflow spans
         List<MockSpan> workflowSpans =
             getSpansByTraceID(spans, spanStartWorkflow.context().toTraceId());
-        MockSpan spanExecuteWF = getLinkedSpans(spans, spanStartWorkflow.context()).get(0);
-        assertEquals(spanExecuteWF.operationName(), "cadence-ExecuteWorkflow");
-        assertSpanReferences(spanExecuteWF, "follows_from", spanStartWorkflow);
+        MockSpan spanExecuteWF =
+            getFirstSpanByOperationName(workflowSpans, "cadence-ExecuteWorkflow");
+        assertChildOf(spans, spanExecuteWF, spanStartWorkflow);
 
         MockSpan spanExecuteActivity = getLinkedSpans(spans, spanExecuteWF.context()).get(0);
         assertEquals(spanExecuteActivity.operationName(), "cadence-ExecuteActivity");
@@ -493,6 +482,15 @@ private void testSignalWithStartWorkflowHelper(
     }
   }
 
+  private MockSpan getFirstSpanByOperationName(List<MockSpan> spans, String operation) {
+    return spans
+        .stream()
+        .filter(span -> span.operationName().equals(operation))
+        .findFirst()
+        .orElseThrow(
+            () -> new IllegalStateException("Failed to find span with operation: " + operation));
+  }
+
   private List<MockSpan> getSpansByTraceID(List<MockSpan> spans, String traceID) {
     return spans
         .stream()
@@ -517,6 +515,27 @@ private List<MockSpan> getLinkedSpans(List<MockSpan> spans, SpanContext spanCont
         .collect(Collectors.toList());
   }
 
+  void assertChildOf(List<MockSpan> spans, MockSpan span, MockSpan parentSpan) {
+    Map<String, MockSpan> byId = new HashMap<>();
+    for (MockSpan s : spans) {
+      byId.put(s.context().traceId() + "-" + s.context().toSpanId(), s);
+    }
+    Queue<MockSpan> toVisit = new LinkedList<>();
+    toVisit.add(span);
+    while (!toVisit.isEmpty()) {
+      MockSpan current = toVisit.poll();
+      MockSpan parent = byId.get(current.context().traceId() + "-" + current.parentId());
+      if (parent != null) {
+        if (parent.equals(parentSpan)) {
+          return;
+        } else {
+          toVisit.add(parent);
+        }
+      }
+    }
+    fail(String.format("span %s is not a child of parent span %s", span, parentSpan));
+  }
+
   void assertSpanReferences(MockSpan span, String referenceType, MockSpan parentSpan) {
     assertTrue(
         String.format(