Fabio Borini and Jermain Defoe scored in quick succession as Sunderland came from behind to boost their Premier League survival hopes by beating 10-man Chelsea 3-2 at the Stadium of Light.
With Norwich City losing to Manchester United earlier on Saturday and Newcastle United held by Aston Villa, Sunderland secured an important three points to move out of the relegation zone.
Sam Allardyce's side started positively but found themselves behind when Diego Costa curled a composed finish beyond Vito Mannone.
A sensational volley from Wahbi Khazri brought Sunderland level, but Nemanja Matic quickly hit back to ensure Chelsea went into the break with an advantage.
Mannone produced a pair of great saves from Costa before two former Chelsea players combined to restore parity, Borini picking out the bottom corner from Patrick van Aanholt's cutback.
Three minutes later Defoe sparked delirium when he put Sunderland ahead, and they held on for a huge win with Chelsea's miserable afternoon completed by the injury-time dismissal of captain John Terry.
Victory over Everton on Wednesday will see Allardyce's team retain their Premier League status and relegate Norwich and Newcastle.
Sunderland, unchanged for the sixth straight Premier League match, were roared on by the home faithful as they immediately deployed a high press that led to Gary Cahill being shown a yellow card inside the first minute for bringing down Defoe.
Eden Hazard was restored to the line-up in place of Pedro following his galvanising display in the 2-2 draw with Tottenham on Monday, and his pass from the left found Cahill, whose attempted cutback deflected off DeAndre Yedlin and fell kindly for Costa to bend it inside the far post with 14 minutes on the clock.
Yedlin had a tame header kept out by the returning Thibaut Courtois, but the Belgian could do nothing when Khazri showed brilliant technique to slam a sublime 20-yard volley into the top corner in the 41st minute.
However, they were unable to hold out until half-time as Cesc Fabregas' looping ball forward was nodded into the path of Matic by Cesar Azpilicueta, and the Serbian slotted a cool finish beneath Vito Mannone.
Mannone fared better against Costa four minutes into the second half when he blocked the Spain international's strike after a perfectly weighted pass from Hazard.
Lamine Kone was replaced by John O'Shea in the 55th minute due to an injury sustained in the first half, and he quickly came under pressure when Costa forced Mannone into another save after the hour mark.
However, two goals in the space of three minutes turned the match on its head.
With 67 minutes on the clock, Van Aanholt picked out Borini with a brilliant cutback, and he drilled an effort into the bottom-left corner, with Courtois perhaps unsighted and wrongfooted by a deflection off Terry.
Sunderland then led for the first time when Defoe produced a great first touch before rifling the ball beyond Courtois, the striker booked for removing his shirt while celebrating in sheer jubilation.
Mannone palmed Willian's free-kick over the top in the 74th minute and Chelsea's woe was compounded by Terry being shown a second yellow card in stoppage-time after colliding with Khazri, the Blues losing a league match at the Stadium of Light for the first time since October 2000.