Wickham and Borini strikes stun high-flying Blues.
Fabio Borini's penalty against his former club sealed a stunning Easter win at Chelsea as the Black Cats' fighting spirit burned brightly against Jose Mourinho's title-chasers.
Mourinho suffered his first home league defeat in 78 games as Chelsea manager as Sunderland came from behind to secure three priceless points.
And Gus Poyet cut a delighted figure after marking his return to Stamford Bridge with a vital victory.
Samuel Eto'o struck early on to give Chelsea the lead, but the goal didn't knock the Black Cats off their stride as they equalised through Connor Wickham within six minutes of the hosts' opener.
A superb rearguard action, anchored by Wes Brown and John O'Shea, kept the hosts' attacking talent at bay, allowing the visitors to deliver a devastating counter-punch in the closing stages.
Ex-Chelsea man Borini – on loan from Liverpool – cashed in to roll in an ice-cool effort from the penalty spot eight minutes from time after substitute Jozy Altidore was fouled by Cesar Azpilicueta.
The goal ensured Sunderland would build on the point they gained at Manchester City in midweek, and they stuck to their guns and refused to wilt in the face of considerable pressure.
Following an encouraging midweek showing at City, Poyet opted to name an unchanged side for the visit to his former club.
The Uruguayan was making his first return to Stamford Bridge as a boss, having featured in a total of 145 games for the Blues, scoring 49 goals, between 1997 and 2001.
Having been warmly welcomed to the touchline by the crowd, Poyet saw his side create the first chance seven minutes in when Wickham laid a neat ball off into the path of Borini, whose shot whistled just past the post.
But they were behind after 12 minutes as a Willian corner caused chaos in the box and Eto'o got ahead of Lee Cattermole to volley emphatically past a helpless Vito Mannone from eight yards out.
The response, though, was swift. Mark Schwarzer spilled Marcos Alonso's drive from outside the box after a corner was played out to the Spanish defender, and Wickham left the Chelsea defence in his wake to swoop and clip the loose ball into the net.
The striker showed good awareness to net his third goal in two games, taking advantage of the hosts' slow reaction after Schwarzer failed to hold the initial shot.
Boosted by their equaliser, Sunderland came close again when Adam Johnson curled a left-footed effort just wide from the right of goal, while at the other end Chelsea captain John Terry headed in from a set piece - but the offside flag had already gone up long beforehand.
The hosts, looking to overtake leaders Liverpool at the top, turned the screw and Mannone was busy in the Sunderland goal in the build-up to half time, pulling off a string of fine saves.
First he tipped Branislav Ivanovic's close-range header from a 42nd-minute corner onto the crossbar, with the ball bouncing back down and into the stopper's grateful arms.
The Italian then tipped away Nemanja Matic's long-range drive before springing to his feet to deny Mohamed Salah with a reaction save on the follow-up.
Chelsea were well on top and Ramires should have done better when he headed wide of an open goal after racing in to meet a cross from the right.
But Sunderland continued to frustrate the hosts, who saw another good chance go begging three minutes into the second half when Eto'o pulled his low shot inches past the far post having been teed up by Willian on the counter-attack.
Mourinho introduced Demba Ba off the bench as the hosts cranked up the pressure and the Senegalese striker wasted a great chance with 25 minutes to play, spooning his shot horribly wide from 12 yards after meeting Willian's cut-back.
Goalscorer Wickham was substituted moments later, limping off having battled an early knock throughout much of the game. The frontman was replaced by Altidore, with Emanuele Giaccherini also entering the fray in place of Johnson.
Another sub – Chelsea's Fernando Torres – was the hosts' chief threat in the closing stages, scooping an acrobatic overhead kick over the bar before seeing a back-post header well claimed by Mannone.
But for all their possession, Mourinho's side struggled to carve out clear-cut chances and were frustrated time and again by a resolute Sunderland outfit.
Indeed, the visitors sensed that they could get something from the game – and they were handed a chance to do so when Azpilicueta felled Altidore with a rash challenge in the box eight minutes from time.
Borini stepped up to take a pressure-laden kick and duly delivered, sending Schwarzer the wrong way to net his seventh goal of the season.
Chelsea responded and only a fine tip-over from Mannone prevented sub Andre Schurrle from equalising almost immediately with a rising drive from 20 yards.
The home crowd grew increasingly frustrated as the seconds ebbed away, with their side unable to really test Mannone in five minutes of injury time barring a Terry header which was easily claimed by the Sunderland keeper.
Indeed, it was the visitors who came closest to finding the net again when late sub Ondrej Celustka – on for Seb Larsson – teed up Giaccherini who whistled a shot just over the crossbar.
And there was no late drama this time as the Black Cats held out to seal a magnificent victory to cap a memorable week.
Four crucial games remain, starting with a huge home clash with Cardiff City.
- Borges Da Silva
- Santos do Nascimento
- dos Santos Emboada Junior (Ba)
- Salah (Schürrle)
- Eto'o (Torres)
- Brown Yellow
- Johnson (Giaccherini)
- Larsson (Celustka)
- Cattermole Yellow
- Wickham (Altidore)
- Luiz Moreira Marinho
- Yellow Torres