Goals from Nedum Onuoha, Asamoah Gyan and Danny Welbeck gave Sunderland a deserved victory over Barclays Premier League leaders Chelsea at Stamford Bridge.
It was Chelsea's first home defeat since March and their first at the hands of Sunderland since 2001.
The visitors stunned Carlo Ancelotti's side on the stroke of half-time when Onuoha dribbled his way through the home defence to score.
Gyan added the second just after half-time and Welbeck seized on a poor backpass by Ashley Cole in the 87th minute to hand Chelsea their second defeat in three games.
Chelsea went into the game hoping to stretch their lead at the top of the table to five points but they never looked likely of wining this encounter.
The Wearsiders made a solid start and warned Chelsea inside the opening few minutes.
Midfielder Lee Cattermole cleverly intercepted an intended pass from Branislav Ivanovic and played the ball out to Gyan on the left.
The Sunderland striker, who scored the equaliser in their 1-1 against Tottenham in midweek, sent his shot just wide of the far post.
Chelsea, who beat Sunderland 7-2 last season, were struggling to make headway against Steve Bruce's side.
Chelsea's new defensive partnership of Paulo Ferriera and Ivanovic, forced upon them by injuries to captain John Terry and Alex, struggled to cope with the movement of Gyan and Welbeck.
In the 18th minute Chelsea managed to fashion their first real chance when John Mikel Obi put Nicolas Anelka in the clear but he could not control it in time and the opportunity went begging.
Moments later Florent Malouda created an opening for Yury Zhirkov but the Russia international ended his twisting run into the area with a shot that flashed past the far post.
Chelsea midfielder Ramires sent an 18-yard header towards the top corner in the 24th minute but Craig Gordon was able to make the save.
Sunderland defender Michael Turner was booked by referee Chris Foy after he brought down Didier Drogba on the edge of the penalty area in the 28th minute.
The Ivory Coast striker sent a rising free-kick just over the top of the crossbar but Chelsea earned a corner as his effort took a deflection.
His next effort, from 35 yards after Lee Cattermole has brought him down, went straight into the hands of Gordon.
But Chelsea goalkeeper Petr Cech kept the scores level in the 36th minute when Onuoha crossed for Welbeck to head the ball towards the bottom corner.
The Czech keeper dived low to his left to turn the ball around the post.
Sunderland were unlucky not to score from the resulting corner when Kieran Richardson sent a shot across the face of the goal.
Cech was the saviour again in the 38th minute when Gyan put Welbeck through but Cech saved with his feet.
Moments later Welbeck was brought down by Ivanovic when he got ahead of the defence and the Chelsea defender was lucky to get just a yellow card.
But after Cech made another superb double save, Onuoha dribbled through the Chelsea defence to put Sunderland in front. It was the first goal Chelsea had conceded at Stamford Bridge since they hosted Aston Villa in March.
Chelsea's afternoon got worse in the 52nd minute when Sunderland opened up their defence once more and Gyan added the second.
Jordan Henderson collected the ball from Welbeck and put Gyan clear, and the Sunderland striker made no mistake as he slipped the ball beyond Cech.
Chelsea were now rocking and unable to cope with Sunderland's quick passing and movement.
In the 59th minute Welbeck sent a curling effort just wide of the far post as the visitors threatened to add to their lead.
Chelsea had been restricted to a couple of long shots from Drogba and the boos rang out from the home fans when Malouda was replaced by Salomon Kalou.
The home side had rarely threatened in the second-half and Bolo Zenden almost made it three for the visitors when he tried to divert the ball past Cech from close range in the 63rd minute.
Chelsea huffed and puffed in a bid to get themselves back into the game but Anelka was just over with an 18-yard shot in the 86th minute.
And Sunderland made it three in the 87th minute when Chelsea defender Cole's poor back pass was intercepted by Welbeck and the striker kept his cool to beat Cech.