The deal with Google, a unit of Alphabet Inc (GOOGL.O), builds on an existing search partnership Microsoft Corp (MSFT.O) under which Yahoo gets a percentage of revenue from ads displayed on its sites. Yahoo, whose shares were down 1.6 percent in after-hours trading, said the companies have agreed to delay implementation of the deal in the United States to allow the antitrust division of the Department of Justice to review it. Yahoo has been struggling to boost revenue from ad sales in the face of stiff competition from Google and Facebook (FB.O).