London - Jose Mourinho suffered his first ever Premier League defeat at Stamford Bridge as Sunderland delivered a major blow to Chelsea's title hopes with a controversial 2-1 victory on Saturday.
Fabio Borini, on loan from leaders Liverpool, converted a contentious 82nd-minute penalty to secure the win for the league's bottom club.
It sparked furious home protests that ended with assistant coach Rui Faria being dragged away from referee Mike Dean by Mourinho and other members of the home side's back-room staff.
Chelsea were incensed at the decision to award the spot-kick after Sunderland substitute Jozy Altidore had gone down under Cesar Azpilicueta's sliding challenge.
The incident was just one of a number of flashpoints in a highly charged game that could have seen players from both sides sent off, while Chelsea midfielder Ramires could face retrospective action for elbowing Sunderland's Sebastian Larsson.
Ultimately though, Borini's spot-kick proved the difference, after Connor Wickham's 18th-minute strike had cancelled out Samuel Eto'o's 12th-minute opening goal, ending Mourinho's 77-game unbeaten home league run.
The result left Chelsea two points behind Liverpool having played a game more, while bottom club Sunderland boosted their survival hopes by moving to within three points of safety.
There was no sign Mourinho was resting key players before Tuesday's Champions League trip to Atletico Madrid and initially it looked as though the Blues would easily overcome a Sunderland side desperate for points.
It took them just 12 minutes to unpick the visitors' defence, when Eto'o's twisting run took him past John O'Shea before a last-ditch tackle by Santiago Vergini denied the forward a shot on goal.
From the resulting corner, Eto'o connected with a close-range volley that appeared to set Chelsea on their way to three points.
Sunderland had offered little during the opening stages but, just as they had in their 2-2 draw at Manchester City in mid-week, Gus Poyet's side recovered after falling behind and within six minutes they were level.
Rather than float the ball into the area from a left-wing corner, Larsson picked out Marcos Alonso, who was unmarked 30 yards from goal.
The left-back drilled in a powerful low shot that Mark Schwarzer -- deputising for the ill Petr Cech -- failed to hold and Wickham reacted first to slot the rebound home from close range.
- Sunderland weather Chelsea storm -
It was the first goal Chelsea had conceded in 10 home games -- a run dating back to the 3-1 victory over Manchester United in mid-January -- and ensured Schwarzer's day would be remembered for the wrong reasons.
The equaliser knocked the home side out of their stride, but they stepped up the pressure in a frantic spell ahead of the interval.
Vito Mannone saved at the second attempt from Branislav Ivanovic's header after initially pushing the ball against the bar.
And the Sunderland goalkeeper was again called into action when he produced a fine double save to deny Nemanja Matic and Mohamed Salah.
Chelsea's frustration then intensified when they were denied two penalty appeals in quick succession, first when Alonso handled the ball and then when Ramires was barged by Larsson as he looked set to head into an empty goal.
The Blues midfielder then took matters into his own hands by elbowing the Sunderland man off the ball and was fortunate the incident was missed by Dean.
The first half ended with both teams nursing a sense of grievance.
And that contributed to a feisty second period that grew more frantic the longer the stalemate endured.
Eto'o passed up a good chance to restore Chelsea's lead two minutes after the restart when he placed his shot wide after a powerful run by Willian.
But while Sunderland struggled to create chances of their own, their defence stood firm in the face of growing home pressure.
Mourinho introduced both Demba Ba and Fernando Torres in an effort to boost his side's firepower, but both missed chances before Borini was handed the chance to seal an unexpected win.