diff --git a/google-cloud-clients/google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/Publisher.java b/google-cloud-clients/google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/Publisher.java
index 3ed22ab5c263..fe9d28f421fb 100644
--- a/google-cloud-clients/google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/Publisher.java
+++ b/google-cloud-clients/google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/Publisher.java
@@ -231,11 +231,12 @@ public ApiFuture<String> publish(PubsubMessage message) {
         messagesBatches.remove(orderingKey);
       }
       setupAlarm();
-      if (!batchesToSend.isEmpty()) {
-        // TODO: if this is not an ordering keys scenario, will this do anything?
+      // For messages with an ordering key, then we need to publish with messagesBatchLock held in
+      // order to ensure another publish doesn't slip in and send a batch before these batches we
+      // already want to send.
+      if (!batchesToSend.isEmpty() && !orderingKey.isEmpty()) {
         publishAllWithoutInflight();
 
-        // TODO: if this is an ordering keys scenario, is this safe without messagesBatchLock?
         for (final OutstandingBatch batch : batchesToSend) {
           logger.log(Level.FINER, "Scheduling a batch for immediate sending.");
           publishOutstandingBatch(batch);
@@ -246,6 +247,16 @@ public ApiFuture<String> publish(PubsubMessage message) {
     }
 
     messagesWaiter.incrementPendingMessages(1);
+
+    // For messages without ordering keys, it is okay to send batches without holding
+    // messagesBatchLock.
+    if (!batchesToSend.isEmpty() && orderingKey.isEmpty()) {
+      for (final OutstandingBatch batch : batchesToSend) {
+        logger.log(Level.FINER, "Scheduling a batch for immediate sending.");
+        publishOutstandingBatch(batch);
+      }
+    }
+
     return outstandingPublish.publishResult;
   }
 
@@ -318,6 +329,7 @@ public void publishAllOutstanding() {
    * for messages to send, call {@code get} on the futures returned from {@code publish}.
    */
   private void publishAllWithoutInflight() {
+    OutstandingBatch unorderedOutstandingBatch = null;
     messagesBatchLock.lock();
     try {
       Iterator<Map.Entry<String, MessagesBatch>> it = messagesBatches.entrySet().iterator();
@@ -327,8 +339,11 @@ private void publishAllWithoutInflight() {
         String key = entry.getKey();
         if (batch.isEmpty()) {
           it.remove();
-        } else if (key.isEmpty() || !sequentialExecutor.hasTasksInflight(key)) {
-          // TODO: Will this cause a performance problem for non-ordering keys scenarios?
+        } else if (key.isEmpty()) {
+          // We will publish the batch with no ordering key outside messagesBatchLock.
+          unorderedOutstandingBatch = batch.popOutstandingBatch();
+          it.remove();
+        } else if (!sequentialExecutor.hasTasksInflight(key)) {
           publishOutstandingBatch(batch.popOutstandingBatch());
           it.remove();
         }
@@ -336,6 +351,9 @@ private void publishAllWithoutInflight() {
     } finally {
       messagesBatchLock.unlock();
     }
+    if (unorderedOutstandingBatch != null) {
+      publishOutstandingBatch(unorderedOutstandingBatch);
+    }
   }
 
   private ApiFuture<PublishResponse> publishCall(OutstandingBatch outstandingBatch) {