Victor Anichebe struck in the 87th minute as West Bromwich Albion prevented Chelsea from opening up a four-point lead in the English Premier League in a 1-1 draw on Tuesday.
Chelsea were bidding to pull clear of the chasing pack and Serbian defender Branislav Ivanovic put them on course to do that when he slammed home from David Luiz’s back-heel in first-half injury time.
Oscar, Samuel Eto’o and Willian all spurned chances to extend the visitors’ lead and West Brom forward Thievy Bifouma almost punished them with a low shot that flashed across the face of goal in the latter stages.
Jose Mourinho’s side appeared to have escaped, but with three minutes remaining Saido Berahino sent in a cross from the left and Anichebe got in front of Luiz and goalkeeper Petr Cech to head home via the base of the post.
The Nigerian striker’s goal means Chelsea could slip to third place on Wednesday, having only taken over at the summit at the weekend.
Second-place Arsenal will return to the top if they win at home to Manchester United, while third-place Manchester City can leapfrog Chelsea on goal difference by overcoming Sunderland.
West Brom, meanwhile, clambered out of the relegation zone at Sunderland’s expense.
Second-bottom Cardiff City squandered an opportunity to haul themselves towards safety after being held to a 0-0 draw by Aston Villa.
Cardiff hit the woodwork twice in the space of a minute during the first half, with Frazier Campbell and Craig Noone the players denied, in a game that left Ole Gunnar Solskjaer’s side two points below West Brom.
West Ham United eased their own relegation fears with a 2-0 win at home to struggling Norwich City.
The visitors created chances throughout the game, but West Ham went ahead in the 84th minute when centre-back James Collins nodded Mohamed Diame’s left-wing cross past Norwich goalkeeper John Ruddy.
Diame struck with a deflected shot in the fourth minute of injury time to complete a third consecutive victory without conceding a goal for Sam Allardyce’s West Ham, who climbed to 10th place in the table.
In the evening’s other match, Southampton leapfrogged Newcastle United into eighth place, and closed to within two points of defending champions Manchester United, with a 1-0 success at Hull City.
Portuguese defender Jose Fonte settled the game in the 69th minute at the KC Stadium, ramming home at the third attempt after his header was saved by Steve Harper and Jay Rodriguez’s follow-up was blocked.