The summer signing first looked unconvincing as he flapped at the air to leave Cheikhou Kouyate to nod home into an empty net before Mauro Zarate added a second, shooting low from range to leave a flat-footed Cech beaten.
The Gunners poured forward in search of the goals to get them back in the game, with Arsene Wenger introducing Alexis Sanchez as a second-half substitute, but the comeback wasn't forthcoming as the Hammers held on for a shock win.
