Watford showed a never-say-die attitude to come back from two goals down to defeat Slaven Bilic's Hammers side.
The Hammers strolled into a two-goal lead thanks to a double by Michail Antonio before Watford made it 2-2 before half-time through Odion Ighalo and Troy Deeney.
Watford then ensured they picked up their first three points of the season through Etienne Capoue and Jose Holebas.
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Watford midfielder Etienne Capoue continued his fine goalscoring form for the Hornets by scoring his side's third goalWest Ham winger Michail Antonio wheels away in celebration after opening the scoring for his side at the London StadiumThe England new boy (centre) celebrates for the second time of the Premier League encounter after doubling his side's leadWatford striker Odion Ighalo looks to the sky after pulling a goal back with four minutes left on the clock during the first halfTroy Deeney ensured his side went into the half-time interval at 2-2 by scoring in first-half stoppage time
