Watford brought West Ham United`s streak of Premier League success to an abrupt halt with a surprise 2-0 win at the London Stadium on Saturday, thanks to a first-half Troy Deene's penalty and a late Gerard Deulofeu's clincher.
Deeney tucked home his third goal of the season in the half-hour from the spot after Fabian Balbuena had bundled over Roberto Pereyra, the defender injuring himself so badly that he had to leave the field.
The goal came during end-to-end fare as the Hammers had begun to take control in search of a fifth successive league victory.
Lukasz Fabianski had saved his last three penalties but could do nothing to stop Deeney putting the visitors ahead, although the Polish goalkeeper did make a magnificent stop after the break to deny Abdoulaye Doucoure.
West Ham did most of the pressing, though, with Michail Antonio twice heading against the post after the break and Javier Hernandez squandering excellent chances before Deulofeu sealed victory three minutes from time with a sharp finish.
The Spaniard`s goal secured Watford their first away win for over two months and lifted them, temporarily at least, into the top six, three points clear of the Hammers.
Watford goalkeeper Ben Foster again needed to be in fine form to thwart the home side.
"We deserved a little bit more, I think, at least to draw the game.Going a goal behind made it more difficult in that we were playing under pressure. We had three or four clear chances to at least draw the game," said West Ham manager Manuel Pellegrini.
"The penalty gave Watford that impetus. Before the goal we had three very dangerous opportunities and dominated. Once they scored, they were calm while we were more nervous."
Watford manager Javi Gracia was not about to get too giddy about his side`s elevated position in the table.
"We have a lot of games so we don`t have time to speak about our position. We are improving. We started playing well with four wins, after that we have competed well with good and bad results," said the Spaniard.
"At the end of the game today, we got the result we deserved. It was an open game but we deserved the victory.Foster, inevitably, came in for special praise. "The keeper always has a good performance and he gives confidence to the rest of the team," Garcia signed off.