Pantomime villain Deeney helps Watford sink West Ham
West Ham was bidding to win a fifth match in a row but fell behind when Robert Pereyra wriggled free in the penalty area and was caught by a clumsy late challenge from Fabian Balbuena.
Lukasz Fabianski saved Deeney’s previous three spot kicks. This time, though, he had no chance as Deeney blasted the ball into a top corner.
Deeney, relishing his role as pantomime villain at the London Stadium, then celebrated by punching the corner flag out of the ground and goading the West Ham supporters.
West Ham, which had been hoping to climb into the top six, went close when Michail Antonio twice hit the woodwork.
Deulofeu finished off the home team with a low drive in the 87th minute.