Lamine Kone's powerful header helped Sunderland to a vital Barclays Premier League victory over Manchester United to rekindle their survival hopes and pile the pressure on Louis van Gaal.
The January signing from French side Lorient powered Wahbi Khazri's 82nd-minute corner towards David de Gea. The ball then ricocheted between the goalkeeper and Anthony Martial on the line before ending up in the back of the net. It was officially credited as a De Gea own goal.
Earlier Martial had cancelled out Khazri's third-minute opener.
It was the Black Cats' first league victory over United on Wearside since March 1997 and left a crowd of 41,687 with fresh belief that Sam Allardyce can lead the club to safety, while the visitors' hopes of a top-four finish suffered a major blow.
At the end of a difficult week for both managers for vastly different reasons, it was Allardyce's face which broke into a smile with just three minutes gone after full-back Matteo Darmian had upended opposite number Patrick van Aanholt.
Khazri curled the resulting free-kick into the penalty area and although Jermain Defoe failed to make contact, the ball skipped off the surface and evaded David de Gea's outstretched arm before nestling inside the far post.
Sunderland maintained the pace as Khazri led Darmian a merry dance in the early stages, and it took a vital challenge by Chris Smalling to prevent Defoe from extending his side's lead after Lee Cattermole had found him inside the box with an 11th-minute pass.
United belatedly responded, but without creating meaningful chances, and they survived penalty appeals when Khazri's 26th-minute drive struck Morgan Schneiderlin's arm, and the Tunisia international fired high and wide after being played in by Defoe two minutes later.
The visitors mustered their first attempt on goal 14 minutes before the break when Juan Mata steered a first-time effort from Wayne Rooney's pass straight into keeper Vito Mannone's midriff, but having lost Darmian to injury, they got themselves back on level terms with six minutes of the half remaining.
Mannone got down well to his right to push away Mata's effort, but the ball fell nicely for Martial, who clipped it expertly from a tight angle over the Italian and into the net.
Defoe was almost presented with an opportunity to restore the Black Cat's lead when Cattermole's 47th-minute shot was only half-blocked and almost dropped into his path, and they were appealing for a penalty - again in vain - when John O'Shea's 50th-minute header from Khazri's corner appeared to striker Rooney's raised hand.
Sunderland were dominating once again and had it not been for Daley Blind's brilliant block, Defoe would have put them ahead from Van Aanholt's cross four minutes later.
De Gea kept United level with 61 minutes gone when he blocked Dame N'Doye's shot with his right boot after Cattermole had picked out the striker's run, and Khazri forced the Spaniard to save from a swerving free-kick after he had been tripped by substitute Donald Love.
De Gea had to tip Kone's stinging drive over five minutes later as an end-to-end encounter entered its final stages, but there was nothing he could do to stop the same man eight minutes from time when he met Khazri's corner with a powerful downward header that ended up in the back of the net.
TWEET OF THE MATCH
"John O'shea man of the match...agree with the @btsport guys.... @ManUtd needed to win this...frustrating watching." Former Manchester United captain Rio Ferdinand (@rioferdy5) was quick to applaud his former team-mate but was not happy to see the Red Devils lose ground on the top four.
Vito Mannone: 6
DeAndre Yedlin: 6
John O'Shea (Capt): 7
Lamine Kone: 7
Patrick van Aanholt: 7
Jan Kirchhoff (Rodwell, 15 mins): 6
Yann M'Vila: 7
Lee Cattermole (Toivonen, 85 mins): 7
Wahbi Khazri: 8
Dame N'Doye: 7
Jermain Defoe (Borini, 71 mins): 7
Jack Rodwell: 6
Fabio Borini: 6
Ola Toivonen: 6
David de Gea: 6
Cameron Borthwick-Jackson: 6
Chris Smalling: 7
Daley Blind: 7
Matteo Darmian (Love, 38 mins): 4
Michael Carrick: 6
Morgan Schneiderlin (Keane, 86 mins): 6
Juan Mata: 7
Jesse Lingard (Depay, 63 mins): 6
Wayne Rooney (Capt): 6
Anthony Martial: 7
Donald Love: 6
Memphis Depay: 6
Will Keane: 6
Wahbi Khazri, Sunderland's £9million January signing, turned in another fine individual display, scoring the first goal, setting up the winner and contributing throughout.
MOMENT OF THE MATCH
Anthony Martial's deft 39th-minute finish after keeper Vito Mannone had parried Juan Mata's effort was as exquisite as it was vital, although ultimately it counted for nothing.
VIEW FROM THE BENCH
Sunderland boss Sam Allardyce got exactly what he wanted in terms of both performance and result from his players ahead of their mid-season trip to Dubai. Louis van Gaal will have been frustrated with his team's inability to impose itself for long periods.
MOAN OF THE MATCH
Allardyce was left to bemoan Jan Kirchhoff's premature departure through injury with an eventful start to his career on Wearside showing few signs of abating.
WHO'S UP NEXT
West Ham v Sunderland, Barclays Premier League, Saturday 27 February
Midtjylland v Manchester United, UEFA Europa League, Thursday 18 February
With 12 Premier League games to go, United's top-four chances look bleak as Van Gaal admitted that winning the Europa League could be their only route into the Champions League.
"I think after this match that is the best route (into the Champions League and that is not so easy because there are a lot of very good teams participating in this event (the Europa League)," he said on BT Sport.
"It will be very difficult now. We give five points away, Chelsea and now this game so it is too much at this time.
"I have to do my work, and I do my work to my utmost best and I must prepare my players for Midtjylland."
When questioned on how disappointing the defeat was, the under-pressure Dutchman said: "I think what I said before the game, you have to win these kind of games and we didn't and we can only blame ourselves.
"Two goals from two set-pieces. They had more aggression than us and we could not cope with that aggression and we don't keep the ball in our possession."
Sunderland boss Allardyce said: "I think the game was similar to (Manchester) City but this time we got what we deserved. The chances we created and the clear-cut one we had was worrying me because we should have been 2-0 up.
"N'Doye was through one-on-one and I was wondering if it would go for us but luckily our new boys helped us out today and it's an unbelievable result for us, beating Manchester United but beating them in the position we're in. This is three big, big bonus points for us."
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