diff --git a/server/src/main/java/org/elasticsearch/action/ingest/SimulateExecutionService.java b/server/src/main/java/org/elasticsearch/action/ingest/SimulateExecutionService.java
index 3f49682183e..aa2e0a893a6 100644
--- a/server/src/main/java/org/elasticsearch/action/ingest/SimulateExecutionService.java
+++ b/server/src/main/java/org/elasticsearch/action/ingest/SimulateExecutionService.java
@@ -67,17 +67,21 @@ class SimulateExecutionService {
     public void execute(SimulatePipelineRequest.Parsed request, ActionListener<SimulatePipelineResponse> listener) {
         threadPool.executor(THREAD_POOL_NAME).execute(ActionRunnable.wrap(listener, l -> {
             final AtomicInteger counter = new AtomicInteger();
-            final List<SimulateDocumentResult> responses = new CopyOnWriteArrayList<>();
+            final List<SimulateDocumentResult> responses =
+                new CopyOnWriteArrayList<>(new SimulateDocumentBaseResult[request.getDocuments().size()]);
+            int iter = 0;
             for (IngestDocument ingestDocument : request.getDocuments()) {
+                final int index = iter;
                 executeDocument(request.getPipeline(), ingestDocument, request.isVerbose(), (response, e) -> {
                     if (response != null) {
-                        responses.add(response);
+                        responses.set(index, response);
                     }
                     if (counter.incrementAndGet() == request.getDocuments().size()) {
                         listener.onResponse(new SimulatePipelineResponse(request.getPipeline().getId(),
                             request.isVerbose(), responses));
                     }
                 });
+                iter++;
             }
         }));
     }
diff --git a/server/src/test/java/org/elasticsearch/action/ingest/SimulateExecutionServiceTests.java b/server/src/test/java/org/elasticsearch/action/ingest/SimulateExecutionServiceTests.java
index 1d1268039d2..43eaad41728 100644
--- a/server/src/test/java/org/elasticsearch/action/ingest/SimulateExecutionServiceTests.java
+++ b/server/src/test/java/org/elasticsearch/action/ingest/SimulateExecutionServiceTests.java
@@ -19,6 +19,9 @@
 
 package org.elasticsearch.action.ingest;
 
+import org.elasticsearch.action.ActionListener;
+import org.elasticsearch.index.VersionType;
+import org.elasticsearch.ingest.AbstractProcessor;
 import org.elasticsearch.ingest.CompoundProcessor;
 import org.elasticsearch.ingest.DropProcessor;
 import org.elasticsearch.ingest.IngestDocument;
@@ -29,18 +32,24 @@ import org.elasticsearch.ingest.RandomDocumentPicks;
 import org.elasticsearch.ingest.TestProcessor;
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.threadpool.TestThreadPool;
-import org.elasticsearch.threadpool.TestThreadPool;
+import org.elasticsearch.threadpool.ThreadPool;
 import org.junit.After;
 import org.junit.Before;
 
+import java.util.ArrayList;
 import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.BiConsumer;
 
 import static org.elasticsearch.ingest.IngestDocumentMatcher.assertIngestDocument;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.instanceOf;
+import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.not;
 import static org.hamcrest.Matchers.notNullValue;
 import static org.hamcrest.Matchers.nullValue;
@@ -331,4 +340,56 @@ public class SimulateExecutionServiceTests extends ESTestCase {
         assertThat(verboseResult.getProcessorResults().get(1).getFailure(), nullValue());
     }
 
+    public void testAsyncSimulation() throws Exception {
+        int numDocs = randomIntBetween(1, 64);
+        List<IngestDocument> documents = new ArrayList<>(numDocs);
+        for (int id = 0; id < numDocs; id++) {
+            documents.add(new IngestDocument("_index", "_type", Integer.toString(id), null, 0L, VersionType.INTERNAL, new HashMap<>()));
+        }
+        Processor processor1 = new AbstractProcessor(null) {
+
+            @Override
+            public void execute(IngestDocument ingestDocument, BiConsumer<IngestDocument, Exception> handler) {
+                threadPool.executor(ThreadPool.Names.GENERIC).execute(() -> {
+                    ingestDocument.setFieldValue("processed", true);
+                    handler.accept(ingestDocument, null);
+                });
+            }
+
+            @Override
+            public IngestDocument execute(IngestDocument ingestDocument) throws Exception {
+                throw new UnsupportedOperationException();
+            }
+
+            @Override
+            public String getType() {
+                return "none-of-your-business";
+            }
+        };
+        Pipeline pipeline = new Pipeline("_id", "_description", version, new CompoundProcessor(processor1));
+        SimulatePipelineRequest.Parsed request = new SimulatePipelineRequest.Parsed(pipeline, documents, false);
+
+        AtomicReference<SimulatePipelineResponse> responseHolder = new AtomicReference<>();
+        AtomicReference<Exception> errorHolder = new AtomicReference<>();
+        CountDownLatch latch = new CountDownLatch(1);
+        executionService.execute(request, ActionListener.wrap(response -> {
+            responseHolder.set(response);
+            latch.countDown();
+        }, e -> {
+            errorHolder.set(e);
+            latch.countDown();
+        }));
+        latch.await(1, TimeUnit.MINUTES);
+        assertThat(errorHolder.get(), nullValue());
+        SimulatePipelineResponse response = responseHolder.get();
+        assertThat(response, notNullValue());
+        assertThat(response.getResults().size(), equalTo(numDocs));
+
+        for (int id = 0; id < numDocs; id++) {
+            SimulateDocumentBaseResult result = (SimulateDocumentBaseResult) response.getResults().get(id);
+            assertThat(result.getIngestDocument().getMetadata().get(IngestDocument.MetaData.ID), equalTo(Integer.toString(id)));
+            assertThat(result.getIngestDocument().getSourceAndMetadata().get("processed"), is(true));
+        }
+    }
+
 }
diff --git a/x-pack/plugin/enrich/src/main/java/org/elasticsearch/xpack/enrich/action/EnrichCoordinatorProxyAction.java b/x-pack/plugin/enrich/src/main/java/org/elasticsearch/xpack/enrich/action/EnrichCoordinatorProxyAction.java
index 7391719c901..06b3b30390c 100644
--- a/x-pack/plugin/enrich/src/main/java/org/elasticsearch/xpack/enrich/action/EnrichCoordinatorProxyAction.java
+++ b/x-pack/plugin/enrich/src/main/java/org/elasticsearch/xpack/enrich/action/EnrichCoordinatorProxyAction.java
@@ -63,7 +63,10 @@ public class EnrichCoordinatorProxyAction extends ActionType<SearchResponse> {
 
         @Override
         protected void doExecute(Task task, SearchRequest request, ActionListener<SearchResponse> listener) {
-            assert Thread.currentThread().getName().contains(ThreadPool.Names.WRITE);
+            // Write tp is expected when executing enrich processor from index / bulk api
+            // Management tp is expected when executing enrich processor from ingest simulate api
+            assert Thread.currentThread().getName().contains(ThreadPool.Names.WRITE)
+                || Thread.currentThread().getName().contains(ThreadPool.Names.MANAGEMENT);
             coordinator.schedule(request, listener);
         }
     }