The Chelsea goalkeeper appeared to have Giorgios Samaras' low cross covered, but the presence of defender Tomas Sivok seemed to distract Cech, who fumbled the ball to allow substitute Theofanis Gekas to roll the loose ball into an empty net.
But Wigan were not going to roll over and they took the lead again when Carmont picked up a loose pass and ran through a large hole in the Dragons defence to score from 60 metres out.