Tottenham's bid to take over at the top of the Premier League was thwarted by West Ham.
Michail Antonio's first-half goal condemned Mauricio Pochettino's in-form side to a 1-0 defeat, their first away from home since the opening day.
Spurs knew victory would take them above Leicester to the summit for the first time this season, as well as send out a huge statement in the race for the title.
Instead they ran into a West Ham side determined not to give their fierce rivals a reason to celebrate in the final London derby under the lights at Upton Park.
The Hammers head to the Olympic Stadium next season but they will miss nights like this with their famous old ground rocking as they ended Tottenham's run of six straight wins.
Antonio will certainly miss the place - all six of his goals for West Ham this season have come at home.
The latest arrived in the seventh minute, when Dimitri Payet swung in a corner and Antonio met it with a powerful near-post header which Hugo Lloris got a hand to but could not keep out.
Tottenham, having become the masters at coming from behind this season, had plenty of time to respond - but this time they could not find a way back.
They were almost two behind after a quarter of an hour but Lloris dived at full stretch to tip away a fierce drive from Mark Noble.
Antonio was denied a second by a last-ditch block from Kevin Wimmer, before James Collins headed another Payet corner narrowly over.
Payet was running through his full repertoire down the Tottenham right and one slide-rule pass - while looking in the opposite direction - almost sent Emmanuel Emenike clean through.
Antonio had the ball in the net again shortly before half-time but there was an offside flag against Emenike.
Spurs, who did not muster a shot on target in the first half, improved after the break but Ben Davies fired wide from the edge of the box and Eric Lamela was off target from Nacer Chadli's cross wide.
They finally tested Hammers goalkeeper Adrian on the hour mark, the Spaniard making a fine save to keep out Toby Alderweireld's shot with Harry Kane unable to convert the rebound.
Kane knew it was not going to be his night when he stretched to reach Christian Eriksen's low cross at the far post only to slice his effort wide.
Instead it was West Ham celebrating a victory which not only dented Spurs' title hopes, but also kept them in the race for an unlikely Champions League spot in this unlikeliest of seasons.
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