Tottenham's title hopes were dealt a decisive blow as Manuel Lanzini's strike gave West Ham a memorable 1-0 win over their London rivals.
Spurs needed a victory to keep the pressure on leaders Chelsea but will now find themselves seven points adrift, with only three games to play, if the Blues beat Middlesbrough at home on Monday.
Such has been their impressive pursuit of Chelsea that Mauricio Pochettino's side arrived at the London Stadium looking for a 10th straight Premier League win.
Few people in either camp would have foreseen any other outcome, either, with West Ham limping towards the finishing line of what has been a torrid season.
Yet it seems there is nothing like a home game against Tottenham to rouse the Hammers and their fans - just a year ago a 1-0 defeat at Upton Park put a major dent in Spurs' eventually unsuccessful title bid.
For all the talk of the lack of atmosphere at West Ham's new home, it crackled early on as some old-fashioned derby tackles went in.
And as Lanzini smashed home the second-half winner, a roar went up like nothing heard at the former Olympic Stadium since Mo Farah came down the final straight in 2012.
For all that it meant to Tottenham, West Ham manager Slaven Bilic had the look of a man with the weight of the world removed from his shoulders as his side ensured they are mathematically safe from relegation.
The victory could also go a long way to keeping Bilic in a job next season.
But for the second season in a row it looks as though Tottenham's title dreams have been shattered, as just two wins for Chelsea will take the title back to Stamford Bridge.
West Ham's game plan was clear from the off, to soak up the Spurs pressure and hopefully hit them on the break.
It almost paid off after just five minutes when a slick counter saw Andre Ayew play in Lanzini but the Argentinian midfielder dragged his shot across goal.
However, the Spurs attack suddenly burst into life when Harry Kane's low drive was beaten out by Adrian, Dele Alli's follow-up was blocked and Adrian recovered to make another fine save to deny Kane.
West Ham's Spanish keeper then frustrated the visitors from the corner for good measure when he kept out Eric Dier's header.
Tottenham hearts were in their mouths moments later when Lanzini raced clear again and was cleaned out by Hugo Lloris on the edge of the area, but the Spurs keeper did get the ball first and referee Anthony Taylor took no action.
Ayew missed a glorious chance to put West Ham ahead after the break when he skied Sam Byram's cut-back from 18 yards.
For Tottenham, the uncharacteristally quiet Christian Eriksen hit a weak shot at Adrian, before the Spaniard tipped a Heung-Min Son shot round his post
But the goal West Ham - and Chelsea - craved arrived in the 65th minute, when Spurs did not deal with Aaron Cresswell's cross.
Byram and Ayew helped the ball on until it rolled to the feet of Lanzini, who gleefully crashed it past Lloris from six yards out.
Spurs pressed for an equaliser but came up short, which looks like being the story of their season for the second year running.