Chelsea 1 Sunderland 2
Fabio Borini, Liverpool’s former Chelsea striker, scored an 81st-minute penalty to take his parent club a step closer to the title.
Borini, on loan at bottom side Sunderland from the Merseysiders, netted from the spot after Cesar Azpilicueta was harshly adjudged to have fouled Jozy Altidore.
It meant a first home league defeat under boss Jose Mourinho for Chelsea, who had taken the lead through Samuel Eto’o before Connor Wickham levelled for the visitors.
And it meant Liverpool, who host the Blues in a vital match next weekend, remained top of the table – and will move five points clear of Mourinho’s team if they beat struggling Norwich on Sunday.
Chelsea, previously unbeaten in 77 home league games under Mourinho, looked comfortable after Eto’o put them ahead by getting in front of his man to volley home Willian’s 12th-minute corner.
But Sunderland equalised six minutes later. Wickham reacted quicker than John Terry and netted from close range after veteran keeper Mark Schwarzer had failed to hold Marcos Alonso’s shot.
Schwarzer, 41, was making his league debut for Chelsea because Petr Cech was laid low by a virus.
After a timid spell, the game exploded back into life during an incident-packed final few minutes of the first half in which Vito Mannone produced a double save, the woodwork was struck, Chelsea appealed in vain for a penalty and Ramires escaped after appearing to elbow Seb Larsson.
The flurry of action began when Sunderland keeper Mannone blocked Branislav Ivanovic’s header from Willian’s corner and the ball looped up on to the bar.
Mannone then kept out Nemanja Matic’s shot and Mo Salah’s follow-up before Alonso was given the benefit of the doubt when the ball hit his hand in the penalty area after rebounding off Borini.
Chelsea again might have had a penalty when Ramires was barged out of the way by Larsson as the midfielder attempted to score into an empty net after Willian’s shot had been parried by Mannone.
Ramires may well have had reason to feel aggrieved but he was then very fortunate referee Mike Dean did not see him lash out at Larsson moments before the interval.
Chelsea made a determined start to the second half and Eto’o shot narrowly wide after being set up by Willian.
Demba Ba, Chelsea’s match-winner in recent victories against Paris St-Germain and Swansea, was brought on just before the hour mark, replacing Oscar.
But Ba missed a glorious chance when he slipped at the crucial moment and sliced wide from eight yards out after exchanging passes with the irrepressible Willian.
Mourinho then threw the dice again, sending on Fernando Torres, who sent an overhead kick over the bar before seeing a header from the edge of the six-yard box saved by Mannone.
Having been under constant pressure, Sunderland were suddenly gifted a chance when Azpilicueta slipped and let in Altidore.
The Black Cats forard seemed to lose his footing as Azpilicueta tried to win the ball back, but Dean felt contact had been made and pointed to the spot.
Borini, who never started a league game during his time at Stamford Bridge, kept his composure to give Sunderland a shock lead they were able to hang onto.
As Chelsea piled forward in search of an equaliser, Andre Schurrle’s powerful drive was pushed over by the impressive Mannone, who also kept out a header from Terry.
Chelsea (4-2-3-1): Schwarzer, Ivanovic, Cahill, Terry, Azpilicueta, Ramires, Matic, Salah (Schurrle 66), Oscar (Ba 59), Willian, Eto’o (Torres 74).
Subs not used: Luiz, Lampard, Mikel, Hilario.