The loss left Spurs, who had been aiming to pull even with fifth-place Everton, in sixth place on 66 points with only one match left in a season in which they had hoped to challenge for a top-four spot.
The visitors dug themselves a hole after 27 minutes when Harry Kane put the ball into his own net. Stewart Downing added the insurance for the Hammers with a left-footed shot to the bottom right corner after a free kick just before halftime.
The result also left Tottenham vulnerable to attack from Manchester United, who were playing strugglers Sunderland later on Saturday.
United have two games in hand on Spurs and a vastly superior goal difference (+20 to +1), meaning that they can guarantee European football, albeit not the Champions League variety they're accustomed to, at Old Trafford next season by winning their remaining games.
The east Londoners have definitely enjoyed their meetings with Spurs this season, having won 3-0 at White Hart Lane in the top flight back in October and then 2-1 at the same ground in the Capital One Cup in December.
But for manager Sam Allardyce, the best part of Saturday's match was the fact that his side kept a clean sheet, something they were excelling at earlier in the season before they started to give up more goals than he wanted to see.