diff --git a/src/core/ext/filters/client_channel/xds/xds_client.cc b/src/core/ext/filters/client_channel/xds/xds_client.cc
index c1954c03ee1..3cdacd79121 100644
--- a/src/core/ext/filters/client_channel/xds/xds_client.cc
+++ b/src/core/ext/filters/client_channel/xds/xds_client.cc
@@ -97,6 +97,7 @@ class XdsClient::ChannelState : public InternallyRefCounted<ChannelState> {
    private:
     void StartNewCallLocked();
     void StartRetryTimerLocked();
+    static void OnRetryTimer(void* arg, grpc_error* error);
     static void OnRetryTimerLocked(void* arg, grpc_error* error);
 
     // The wrapped call that talks to the xds server. It's instantiated
@@ -129,6 +130,8 @@ class XdsClient::ChannelState : public InternallyRefCounted<ChannelState> {
     bool seen_response() const { return seen_response_; }
 
    private:
+    static void OnResponseReceived(void* arg, grpc_error* error);
+    static void OnStatusReceived(void* arg, grpc_error* error);
     static void OnResponseReceivedLocked(void* arg, grpc_error* error);
     static void OnStatusReceivedLocked(void* arg, grpc_error* error);
 
@@ -180,10 +183,6 @@ class XdsClient::ChannelState : public InternallyRefCounted<ChannelState> {
      public:
       Reporter(RefCountedPtr<LrsCallState> parent, grpc_millis report_interval)
           : parent_(std::move(parent)), report_interval_(report_interval) {
-        GRPC_CLOSURE_INIT(&on_next_report_timer_, OnNextReportTimerLocked, this,
-                          grpc_combiner_scheduler(xds_client()->combiner_));
-        GRPC_CLOSURE_INIT(&on_report_done_, OnReportDoneLocked, this,
-                          grpc_combiner_scheduler(xds_client()->combiner_));
         ScheduleNextReportLocked();
       }
 
@@ -191,8 +190,10 @@ class XdsClient::ChannelState : public InternallyRefCounted<ChannelState> {
 
      private:
       void ScheduleNextReportLocked();
+      static void OnNextReportTimer(void* arg, grpc_error* error);
       static void OnNextReportTimerLocked(void* arg, grpc_error* error);
       void SendReportLocked();
+      static void OnReportDone(void* arg, grpc_error* error);
       static void OnReportDoneLocked(void* arg, grpc_error* error);
 
       bool IsCurrentReporterOnCall() const {
@@ -212,6 +213,9 @@ class XdsClient::ChannelState : public InternallyRefCounted<ChannelState> {
       grpc_closure on_report_done_;
     };
 
+    static void OnInitialRequestSent(void* arg, grpc_error* error);
+    static void OnResponseReceived(void* arg, grpc_error* error);
+    static void OnStatusReceived(void* arg, grpc_error* error);
     static void OnInitialRequestSentLocked(void* arg, grpc_error* error);
     static void OnResponseReceivedLocked(void* arg, grpc_error* error);
     static void OnStatusReceivedLocked(void* arg, grpc_error* error);
@@ -449,8 +453,6 @@ XdsClient::ChannelState::RetryableCall<T>::RetryableCall(
               .set_multiplier(GRPC_XDS_RECONNECT_BACKOFF_MULTIPLIER)
               .set_jitter(GRPC_XDS_RECONNECT_JITTER)
               .set_max_backoff(GRPC_XDS_RECONNECT_MAX_BACKOFF_SECONDS * 1000)) {
-  GRPC_CLOSURE_INIT(&on_retry_timer_, OnRetryTimerLocked, this,
-                    grpc_combiner_scheduler(chand_->xds_client()->combiner_));
   StartNewCallLocked();
 }
 
@@ -504,10 +506,21 @@ void XdsClient::ChannelState::RetryableCall<T>::StartRetryTimerLocked() {
             chand()->xds_client(), chand(), timeout);
   }
   this->Ref(DEBUG_LOCATION, "RetryableCall+retry_timer_start").release();
+  GRPC_CLOSURE_INIT(&on_retry_timer_, OnRetryTimer, this,
+                    grpc_schedule_on_exec_ctx);
   grpc_timer_init(&retry_timer_, next_attempt_time, &on_retry_timer_);
   retry_timer_callback_pending_ = true;
 }
 
+template <typename T>
+void XdsClient::ChannelState::RetryableCall<T>::OnRetryTimer(
+    void* arg, grpc_error* error) {
+  RetryableCall* calld = static_cast<RetryableCall*>(arg);
+  calld->chand_->xds_client()->combiner()->Run(
+      GRPC_CLOSURE_INIT(&on_retry_timer_, OnRetryTimerLocked, this, nullptr),
+      GRPC_ERROR_REF(error));
+}
+
 template <typename T>
 void XdsClient::ChannelState::RetryableCall<T>::OnRetryTimerLocked(
     void* arg, grpc_error* error) {
@@ -555,10 +568,6 @@ XdsClient::ChannelState::AdsCallState::AdsCallState(
   // Init other data associated with the call.
   grpc_metadata_array_init(&initial_metadata_recv_);
   grpc_metadata_array_init(&trailing_metadata_recv_);
-  GRPC_CLOSURE_INIT(&on_response_received_, OnResponseReceivedLocked, this,
-                    grpc_combiner_scheduler(xds_client()->combiner_));
-  GRPC_CLOSURE_INIT(&on_status_received_, OnStatusReceivedLocked, this,
-                    grpc_combiner_scheduler(xds_client()->combiner_));
   // Start the call.
   if (GRPC_TRACE_FLAG_ENABLED(grpc_xds_client_trace)) {
     gpr_log(GPR_INFO,
@@ -602,6 +611,8 @@ XdsClient::ChannelState::AdsCallState::AdsCallState(
   op->reserved = nullptr;
   op++;
   Ref(DEBUG_LOCATION, "ADS+OnResponseReceivedLocked").release();
+  GRPC_CLOSURE_INIT(&on_response_received_, OnResponseReceived, this,
+                    grpc_schedule_on_exec_ctx);
   call_error = grpc_call_start_batch_and_execute(call_, ops, (size_t)(op - ops),
                                                  &on_response_received_);
   GPR_ASSERT(GRPC_CALL_OK == call_error);
@@ -617,6 +628,9 @@ XdsClient::ChannelState::AdsCallState::AdsCallState(
   // This callback signals the end of the call, so it relies on the initial
   // ref instead of a new ref. When it's invoked, it's the initial ref that is
   // unreffed.
+
+  GRPC_CLOSURE_INIT(&on_status_received_, OnStatusReceived, this,
+                    grpc_schedule_on_exec_ctx);
   call_error = grpc_call_start_batch_and_execute(call_, ops, (size_t)(op - ops),
                                                  &on_status_received_);
   GPR_ASSERT(GRPC_CALL_OK == call_error);
@@ -643,6 +657,16 @@ void XdsClient::ChannelState::AdsCallState::Orphan() {
   // corresponding unref happens in on_status_received_ instead of here.
 }
 
+void XdsClient::ChannelState::AdsCallState::OnResponseReceived(
+    void* arg, grpc_error* error) {
+  AdsCallState* ads_calld = static_cast<AdsCallState*>(arg);
+  ads_calld->xds_client()->combiner_->Run(
+      GRPC_CLOSURE_INIT(&on_response_received_, OnResponseReceivedLocked, this,
+                        nullptr),
+      GRPC_ERROR_REF(error));
+  ;
+}
+
 void XdsClient::ChannelState::AdsCallState::OnResponseReceivedLocked(
     void* arg, grpc_error* error) {
   AdsCallState* ads_calld = static_cast<AdsCallState*>(arg);
@@ -786,6 +810,15 @@ void XdsClient::ChannelState::AdsCallState::OnResponseReceivedLocked(
   GPR_ASSERT(GRPC_CALL_OK == call_error);
 }
 
+void XdsClient::ChannelState::AdsCallState::OnStatusReceived(
+    void* arg, grpc_error* error) {
+  AdsCallState* ads_calld = static_cast<AdsCallState*>(arg);
+  ads_calld->xds_client()->combiner_->Run(
+      GRPC_CLOSURE_INIT(&on_status_received_, OnStatusReceivedLocked, this,
+                        nullptr),
+      GRPC_ERROR_REF(error));
+}
+
 void XdsClient::ChannelState::AdsCallState::OnStatusReceivedLocked(
     void* arg, grpc_error* error) {
   AdsCallState* ads_calld = static_cast<AdsCallState*>(arg);
@@ -831,11 +864,22 @@ void XdsClient::ChannelState::LrsCallState::Reporter::Orphan() {
 void XdsClient::ChannelState::LrsCallState::Reporter::
     ScheduleNextReportLocked() {
   const grpc_millis next_report_time = ExecCtx::Get()->Now() + report_interval_;
+  GRPC_CLOSURE_INIT(&on_next_report_timer_, OnNextReportTimer, this,
+                    grpc_schedule_on_exec_ctx);
   grpc_timer_init(&next_report_timer_, next_report_time,
                   &on_next_report_timer_);
   next_report_timer_callback_pending_ = true;
 }
 
+void XdsClient::ChannelState::LrsCallState::Reporter::OnNextReportTimer(
+    void* arg, grpc_error* error) {
+  Reporter* self = static_cast<Reporter*>(arg);
+  self->xds_client()->combiner()->Run(
+      GRPC_CLOSURE_INIT(&on_next_report_timer_, OnNextReportTimerLocked, this,
+                        nullptr),
+      GRPC_ERROR_REF(error));
+}
+
 void XdsClient::ChannelState::LrsCallState::Reporter::OnNextReportTimerLocked(
     void* arg, grpc_error* error) {
   Reporter* self = static_cast<Reporter*>(arg);
@@ -875,6 +919,8 @@ void XdsClient::ChannelState::LrsCallState::Reporter::SendReportLocked() {
   memset(&op, 0, sizeof(op));
   op.op = GRPC_OP_SEND_MESSAGE;
   op.data.send_message.send_message = parent_->send_message_payload_;
+  GRPC_CLOSURE_INIT(&on_report_done_, OnReportDone, this,
+                    grpc_schedule_on_exec_ctx);
   grpc_call_error call_error = grpc_call_start_batch_and_execute(
       parent_->call_, &op, 1, &on_report_done_);
   if (GPR_UNLIKELY(call_error != GRPC_CALL_OK)) {
@@ -885,6 +931,14 @@ void XdsClient::ChannelState::LrsCallState::Reporter::SendReportLocked() {
   }
 }
 
+void XdsClient::ChannelState::LrsCallState::Reporter::OnReportDone(
+    void* arg, grpc_error* error) {
+  Reporter* self = static_cast<Reporter*>(arg);
+  self->xds_client()->combiner_->Run(
+      GRPC_CLOSURE_INIT(&on_report_done_, OnReportDoneLocked, this, nullptr),
+      GRPC_ERROR_REF(error));
+}
+
 void XdsClient::ChannelState::LrsCallState::Reporter::OnReportDoneLocked(
     void* arg, grpc_error* error) {
   Reporter* self = static_cast<Reporter*>(arg);
@@ -931,12 +985,7 @@ XdsClient::ChannelState::LrsCallState::LrsCallState(
   // Init other data associated with the LRS call.
   grpc_metadata_array_init(&initial_metadata_recv_);
   grpc_metadata_array_init(&trailing_metadata_recv_);
-  GRPC_CLOSURE_INIT(&on_initial_request_sent_, OnInitialRequestSentLocked, this,
-                    grpc_combiner_scheduler(xds_client()->combiner_));
-  GRPC_CLOSURE_INIT(&on_response_received_, OnResponseReceivedLocked, this,
-                    grpc_combiner_scheduler(xds_client()->combiner_));
-  GRPC_CLOSURE_INIT(&on_status_received_, OnStatusReceivedLocked, this,
-                    grpc_combiner_scheduler(xds_client()->combiner_));
+
   // Start the call.
   if (GRPC_TRACE_FLAG_ENABLED(grpc_xds_client_trace)) {
     gpr_log(GPR_INFO,
@@ -963,6 +1012,8 @@ XdsClient::ChannelState::LrsCallState::LrsCallState(
   op->reserved = nullptr;
   op++;
   Ref(DEBUG_LOCATION, "LRS+OnInitialRequestSentLocked").release();
+  GRPC_CLOSURE_INIT(&on_initial_request_sent_, OnInitialRequestSent, this,
+                    grpc_schedule_on_exec_ctx);
   call_error = grpc_call_start_batch_and_execute(call_, ops, (size_t)(op - ops),
                                                  &on_initial_request_sent_);
   GPR_ASSERT(GRPC_CALL_OK == call_error);
@@ -981,6 +1032,8 @@ XdsClient::ChannelState::LrsCallState::LrsCallState(
   op->reserved = nullptr;
   op++;
   Ref(DEBUG_LOCATION, "LRS+OnResponseReceivedLocked").release();
+  GRPC_CLOSURE_INIT(&on_response_received_, OnResponseReceived, this,
+                    grpc_schedule_on_exec_ctx);
   call_error = grpc_call_start_batch_and_execute(call_, ops, (size_t)(op - ops),
                                                  &on_response_received_);
   GPR_ASSERT(GRPC_CALL_OK == call_error);
@@ -996,6 +1049,8 @@ XdsClient::ChannelState::LrsCallState::LrsCallState(
   // This callback signals the end of the call, so it relies on the initial
   // ref instead of a new ref. When it's invoked, it's the initial ref that is
   // unreffed.
+  GRPC_CLOSURE_INIT(&on_status_received_, OnStatusReceived, this,
+                    grpc_schedule_on_exec_ctx);
   call_error = grpc_call_start_batch_and_execute(call_, ops, (size_t)(op - ops),
                                                  &on_status_received_);
   GPR_ASSERT(GRPC_CALL_OK == call_error);
@@ -1044,6 +1099,15 @@ void XdsClient::ChannelState::LrsCallState::MaybeStartReportingLocked() {
       Ref(DEBUG_LOCATION, "LRS+load_report+start"), load_reporting_interval_);
 }
 
+void XdsClient::ChannelState::LrsCallState::OnInitialRequestSent(
+    void* arg, grpc_error* error) {
+  LrsCallState* lrs_calld = static_cast<LrsCallState*>(arg);
+  lrs_calld->xds_client()->combiner_->Run(
+      GRPC_CLOSURE_INIT(&on_initial_request_sent_, OnInitialRequestSentLocked,
+                        this, nullptr),
+      GRPC_ERROR_REF(error));
+}
+
 void XdsClient::ChannelState::LrsCallState::OnInitialRequestSentLocked(
     void* arg, grpc_error* error) {
   LrsCallState* lrs_calld = static_cast<LrsCallState*>(arg);
@@ -1054,6 +1118,15 @@ void XdsClient::ChannelState::LrsCallState::OnInitialRequestSentLocked(
   lrs_calld->Unref(DEBUG_LOCATION, "LRS+OnInitialRequestSentLocked");
 }
 
+void XdsClient::ChannelState::LrsCallState::OnResponseReceived(
+    void* arg, grpc_error* error) {
+  LrsCallState* lrs_calld = static_cast<LrsCallState*>(arg);
+  lrs_calld->xds_client()->combiner_->Run(
+      GRPC_CLOSURE_INIT(&on_response_received_, OnResponseReceivedLocked, this,
+                        nullptr),
+      GRPC_ERROR_REF(error));
+}
+
 void XdsClient::ChannelState::LrsCallState::OnResponseReceivedLocked(
     void* arg, grpc_error* error) {
   LrsCallState* lrs_calld = static_cast<LrsCallState*>(arg);
@@ -1137,11 +1210,22 @@ void XdsClient::ChannelState::LrsCallState::OnResponseReceivedLocked(
   op.reserved = nullptr;
   GPR_ASSERT(lrs_calld->call_ != nullptr);
   // Reuse the "OnResponseReceivedLocked" ref taken in ctor.
+  GRPC_CLOSURE_INIT(&on_response_received_, OnResponseReceived, this,
+                    grpc_schedule_on_exec_ctx);
   const grpc_call_error call_error = grpc_call_start_batch_and_execute(
       lrs_calld->call_, &op, 1, &lrs_calld->on_response_received_);
   GPR_ASSERT(GRPC_CALL_OK == call_error);
 }
 
+void XdsClient::ChannelState::LrsCallState::OnStatusReceived(
+    void* arg, grpc_error* error) {
+  LrsCallState* lrs_calld = static_cast<LrsCallState*>(arg);
+  lrs_calld->xds_client()->combiner_->Run(
+      GRPC_CLOSURE_INIT(&on_status_received_, OnStatusReceivedLocked, this,
+                        nullptr),
+      GRPC_ERROR_REF(error));
+}
+
 void XdsClient::ChannelState::LrsCallState::OnStatusReceivedLocked(
     void* arg, grpc_error* error) {
   LrsCallState* lrs_calld = static_cast<LrsCallState*>(arg);
diff --git a/src/core/ext/filters/client_channel/xds/xds_client.h b/src/core/ext/filters/client_channel/xds/xds_client.h
index ef4210acb3d..5de6c37ad18 100644
--- a/src/core/ext/filters/client_channel/xds/xds_client.h
+++ b/src/core/ext/filters/client_channel/xds/xds_client.h
@@ -108,6 +108,8 @@ class XdsClient : public InternallyRefCounted<XdsClient> {
   static RefCountedPtr<XdsClient> GetFromChannelArgs(
       const grpc_channel_args& args);
 
+  grpc_combiner* combiner() { return combiner_; }
+
  private:
   class ChannelState;