A goal with two minutes to go from Elliot Embleton gave Sunderland a priceless win over the U's this afternoon that leaves United trailing the play-off pack with games running out.
Elliott Moore's powerful header had levelled an entertaining game after Corry Evans had given the visitors an early lead but, as United pressed for a winner Embleton fired home to break the hearts of a sell-out home crowd.
Considering the situation, nobody seemed to tell the two sides it was meant to be tense and the first half in particular was ferociously end to end.
Mark Sykes saw a drive saved by visiting keeper Anthony Patterson after just two minutes and blasted another over the fence a few minutes later, while at the other end Nathan Broadhead was denied by the broad boot of the immense Luke McNally when he seemed sure to score.
The return of captain Moore and the highly influential Cameron Brannagan gave United a touch more stability, and they moved the ball smartly on the sunlit Kassam Stadium pitch all afternoon, backed by a vociferous home following, but sometimes you need a break of the ball and on 16 minutes that went the way of the visiting side.
United’s wall repelled a free kick, they blocked the follow up from Jay Matete, but the ball broke the way of captain Evans who turned and poked it past the helpless Jack Stevens for the opener.
No matter. The ever-resilient United just stuck to their guns and slowly took over the rest of the half.
On 35 minutes they were deservedly level when Moore marked his return with a thumping header to power Billy Bodin’s free kick past the helpless Patterson, and the pattern had been set - United pressing Sunderland back but very aware of the threat they posed on the break.
That continued after the break. Matete don't text* but did shoot and forced Stevens into early handling practice, but the marauding McNally was more threatening moments later with a low drive that flashed just the wrong side of the left post.
With Man-of-the-Match Ciaron Brown having a fine game at left-back and Sam Long terrific on the other side, United's back line looked strong - Matete's speculative effort and the goal were Sunderland's only efforts on target in the first hour - but the question from that point on was whether either side would gamble, knowing a draw would suit other teams more than them?
Sunderland seemed to take the safer option - understandable with a game in hand - but that was annoyingly deceptive.
For the second time this week, the opposition keeper made a magnificent, match-defining, save, Patterson somehow clawing away Brown's back-post header on 66 minutes, and although a Bodin free kick clipped the top of the bar with 15 minutes left, United could find no further way through.
And then it all went wrong.
Two minutes to go and the excellent Matete drove the away side forward. The ball was flicked on to Embleton and he smashed it joyfully past the exposed Stevens to win the game.
The season isn't over, it just got harder.
Four games left and United probably need to win all four. See you at Fleetwood...
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Report by Chris Williams, pictures by Steve Daniels, Steve Edmunds and Rex Shutterstock, stats by OPTA
*Too obscure? Email Dannytrejo@oufc.co.uk with your complaints