Trevor Sinclair and Frederic Kanoute scored for the Hammers, while Darius Vassell and substitute Oyvind Leonhardsen netted for Villa.
Birmingham's victory over Sunderland took them to 38 points, but Bolton failed to improve on their tally after losing 1-0 at Chelsea, for whom Carlton Cole scored the 58th minute winner.
Bolton host West Ham in a vital match next weekend, with defeat for the Hammers likely to signal the end of 10 years' top-flight football at Upton Park.
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