diff --git a/lighthouse-core/config/default.json b/lighthouse-core/config/default.json
index ca03fd3b4b8f..82483dc07f48 100644
--- a/lighthouse-core/config/default.json
+++ b/lighthouse-core/config/default.json
@@ -18,6 +18,7 @@
   },
   {
     "loadPage": true,
+    "network": true,
     "gatherers": [
       "service-worker",
       "offline"
diff --git a/lighthouse-core/gather/gatherers/offline.js b/lighthouse-core/gather/gatherers/offline.js
index 34e87e7bb726..b13fb553704d 100644
--- a/lighthouse-core/gather/gatherers/offline.js
+++ b/lighthouse-core/gather/gatherers/offline.js
@@ -15,27 +15,10 @@
  * limitations under the License.
  */
 
-/* global XMLHttpRequest, __returnResults */
-
 'use strict';
 
 const Gatherer = require('./gatherer');
 
-// *WARNING* do not use fetch.. due to it requiring window focus to fire.
-// Request the current page by issuing a XMLHttpRequest request to ''
-// and storing the status code on the window.
-// This runs in the context of the page, so we don't cover it with unit tests.
-/* istanbul ignore next */
-const requestPage = function() {
-  const oReq = new XMLHttpRequest();
-  oReq.onload = oReq.onerror = e => {
-    // __returnResults is injected by driver.evaluateAsync
-    __returnResults(e.currentTarget.status);
-  };
-  oReq.open('GET', '');
-  oReq.send();
-};
-
 class Offline extends Gatherer {
 
   static config(opts) {
@@ -59,23 +42,28 @@ class Offline extends Gatherer {
     return driver.sendCommand('Network.emulateNetworkConditions', Offline.config({offline: false}));
   }
 
-  afterPass(options) {
+  beforePass(options) {
     const driver = options.driver;
 
-    // TODO eventually we will want to walk all network
-    // requests that the page initially made and retry them.
-    return Offline
-        .goOffline(driver)
-        .then(_ => driver.evaluateAsync(`(${requestPage.toString()}())`))
-        .then(offlineResponseCode => {
-          this.artifact = offlineResponseCode;
-        })
-        .then(_ => Offline.goOnline(driver))
-        .catch(_ => {
-          this.artifact = {
-            offlineResponseCode: -1
-          };
-        });
+    return driver.gotoURL(options.url, {waitForLoad: true})
+      .then(_ => Offline.goOffline(driver))
+      // Navigate away, then back, to allow a service worker that doesn't call
+      // clients.claim() to take control of the page load.
+      .then(_ => driver.gotoURL('about:blank'))
+      .then(_ => driver.gotoURL(options.url, {waitForLoad: true}))
+      .then(_ => Offline.goOnline(driver));
+  }
+
+  afterPass(options, tracingData) {
+    const navigationRecord = tracingData.networkRecords.filter(record => {
+      // If options.url is just an origin without a path, the Chrome will
+      // implicitly add in a path of '/'.
+      return (record._url === options.url || record._url === options.url + '/') &&
+        record._initiator.type === 'other' &&
+        record._fetchedViaServiceWorker;
+    })[0];
+
+    this.artifact = navigationRecord ? navigationRecord.statusCode : -1;
   }
 }
 
diff --git a/lighthouse-core/lib/network-recorder.js b/lighthouse-core/lib/network-recorder.js
index 9b8903db108d..1b6cff9a4f0c 100644
--- a/lighthouse-core/lib/network-recorder.js
+++ b/lighthouse-core/lib/network-recorder.js
@@ -87,8 +87,14 @@ class NetworkRecorder extends EventEmitter {
   }
 
   onResourceChangedPriority(data) {
-    this.networkManager._dispatcher.resourceChangedPriority(data.requestId,
-      data.newPriority, data.timestamp);
+    // TODO: this.networkManager._dispatcher.resourceChangedPriority is set to
+    // undefined when onResourceChangedPriority is triggered in
+    // gatherers/offline.js. The underlying cause may need to be investigated.
+    // In the meantime, explicitly check that it's a function.
+    if (typeof this.networkManager._dispatcher.resourceChangedPriority === 'function') {
+      this.networkManager._dispatcher.resourceChangedPriority(data.requestId,
+        data.newPriority, data.timestamp);
+    }
   }
 
   static recordsFromLogs(logs) {
diff --git a/lighthouse-core/test/gather/gatherers/offline-test.js b/lighthouse-core/test/gather/gatherers/offline-test.js
index aed67e2fb63a..c6a5a88d2cdb 100644
--- a/lighthouse-core/test/gather/gatherers/offline-test.js
+++ b/lighthouse-core/test/gather/gatherers/offline-test.js
@@ -55,21 +55,4 @@ describe('HTTP Redirect gatherer', () => {
       assert.deepEqual(offlineGather.artifact, {offlineResponseCode: -1});
     });
   });
-
-  it('handles driver evaluateAsync() failure', () => {
-    return offlineGather.afterPass({
-      driver: {
-        sendCommand() {
-          return Promise.resolve();
-        },
-        evaluateAsync() {
-          return Promise.reject();
-        }
-      }
-    }).then(_ => {
-      assert(false);
-    }).catch(_ => {
-      assert.deepEqual(offlineGather.artifact, {offlineResponseCode: -1});
-    });
-  });
 });