diff --git a/lib/harAnalyzer.js b/lib/harAnalyzer.js
index 9cdff66..7074f09 100644
--- a/lib/harAnalyzer.js
+++ b/lib/harAnalyzer.js
@@ -149,18 +149,51 @@ export class HarAnalyzer {
   // HAR -> simplified data
   // ---------------------------------------------------------------------------
 
-  transform2SimplifiedData(harData, navUrl) {
-    const data = { url: navUrl, primary: null, htmls: [] };
-
+  getFirstPageEntries(navUrl, harData) {
     let log = harData;
     if (log && 'log' in log) {
       log = log.log;
     }
     if (!log || !Array.isArray(log.entries)) {
-      return data;
+      return [];
+    }
+    const entries = log.entries;
+
+    // A HAR can contain more than one page, for example when a concurrent
+    // browsertime run ends up in the same browser session (crossed DevTools
+    // port) and navigates to another website mid-recording. Requests made
+    // by other pages must not be attributed to the tested website, and if
+    // the recording doesn't even start with the navigated url's host nothing
+    // in it can be trusted.
+    if (navUrl && entries.length > 0) {
+      const firstUrl = entries[0].request && entries[0].request.url;
+      if (firstUrl) {
+        try {
+          if (new URL(firstUrl).hostname !== new URL(navUrl).hostname) {
+            return [];
+          }
+        } catch {
+          // Unparsable URLs are handled by the entry loops as before
+        }
+      }
     }
 
-    for (const entry of log.entries) {
+    const pages = log.pages;
+    if (!Array.isArray(pages) || pages.length === 0) {
+      return entries;
+    }
+    const firstPageId = pages[0].id;
+    if (firstPageId === undefined) {
+      return entries;
+    }
+    return entries.filter(entry =>
+      entry.pageref === undefined || entry.pageref === firstPageId);
+  }
+
+  transform2SimplifiedData(harData, navUrl) {
+    const data = { url: navUrl, primary: null, htmls: [] };
+
+    for (const entry of this.getFirstPageEntries(navUrl, harData)) {
       const req = entry.request || {};
       const res = entry.response || {};
       const content = res.content || {};