Manchester United suffered a further setback in the race for the top four as David de Gea's own goal gave relegation-threatened Sunderland a 2-1 Premier League victory at the Stadium of Light.
Louis van Gaal admitted that last week's dropped points at Chelsea could prove costly in the race for the Champions League places and his side were again made to pay by an energetic Sunderland on Saturday.
Sunderland had never before beaten United at the Stadium of Light in the top flight, but gave themselves the platform to end that run when Wahbi Khazri's free-kick bounced through the crowded area and into the net after just three minutes.
United looked uncomfortable against a high-pressing home side and suffered another blow when Matteo Darmian went off with a shoulder injury, but Anthony Martial snatched an equaliser just before half-time.
Sam Allardyce's men were the more threatening side for much of the second half and only two fine saves from De Gea denied the hosts the lead for the second time in what proved to be an end-to-end second 45 minutes.
The game looked set to end as a stalemate until Lamine Kone powered a header goalwards which rebounded in off De Gea with just seven minutes to play to give Sunderland a massive boost in their bid for survival and leave United's top-four hopes looking increasingly bleak.
It did not take Sunderland long to break the deadlock, albeit in fortuitous circumstances. Khazri's low free-kick from the left evaded Jermain Defoe's attempted flick and bounced all the way into the far corner past De Gea's despairing dive.
Defoe missed a great chance to make it 2-0 when Chris Smalling intervened to deny him a tap-in as United found it difficult to create space against a Sunderland side buoyed by their early goal, though Juan Mata fired their best chance of the opening half hour straight at Vito Mannone from 18 yards.
But more superb work from Mannone proved to be in vain as United grabbed a 39th-minute equaliser. The Italian reacted superbly to keep Mata's low effort out of the bottom corner, but Martial turned home the rebound with a clever chipped finish from a tight angle.
Sunderland started the second half brightly and saw penalty appeals waved away by referee Andre Marriner after John O'Shea's header came off Wayne Rooney's raised arm and Defoe spurned a glorious chance regain the lead when he failed to connect with Patrick van Aanholt's cross just a few feet from the near post.
Dame N'Doye sprung the offside trap to race clean through on goal, but De Gea denied him with an outstretched foot as Sunderland continued to look the more likely, although Jack Rodwell had to time his block perfectly to thwart Mata from inside the area.
Kone forced De Gea into another strong stop at his near post after bending an effort towards the top corner as the game began to open up, with Smalling coming close to heading home Rooney's cross at the far post as United stepped up their own efforts to find a winner.
Substitute Memphis Depay placed a shot straight at Mannone from inside the area, but Kone finally found a way to win it for Sunderland, rising completely unmarked from a corner to power a header through the grasp of the goalkeeper, with the ball going in off the Spain international's back after Martial tried to hook it clear on the line.