Manchester United's burgeoning title charge suffered a shock blow as they were beaten 2-1 by rock-bottom Sheffield United at Old Trafford.
The visitors claimed only their second Premier League win of the campaign and condemned United to their first league defeat since November thanks to goals from Kean Bryan and Oliver Burke.
Those strikes came either side of a Harry Maguire header that would have had the hosts expecting another of the comebacks that have been their trademark during a strong start to the season.
But there was no such turnaround, Chris Wilder's side taking a hard-fought three points on Wednesday evening.
Ole Gunnar Solskjaer's starting XI showed six changes from the weekend FA Cup win over Liverpool but United showed no lack of fluency in the initial stages at least.
The hosts went close when Aaron Wan-Bissaka picked out Marcus Rashford with a pull-back to the edge of the area, the striker sending a low effort just past the post.
However, the visitors responded instantly, Billy Sharp forcing David De Gea into a trademark save with his legs after sneaking in behind the Manchester United defence.
And they took the lead moments later, Bryan heading in off the far post after rising highest to meet a John Fleck's teasing corner delivery, perhaps being helped by what looked like a Sharp push on De Gea.
If United were feeling hard done to by that call, their mood will not have been helped when an immediate reply from Anthony Martial was ruled out for a push on Sheffield United goalkeeper Aaron Ramsdale that looked soft on second viewing.
Still, if nothing else, the visitors' half-time lead had provided another test of United's oft-doubted title credentials, and they looked desperate to pass it judging by their start to the second half.
Turning that desire into clear cut opportunities was proving difficult for large parts, but Solskjaer's men finally got their leveller just past the hour mark as Maguire headed in from an Alex Telles corner.
When that goal was followed by the introduction of Edinson Cavani off the bench, Sheffield United fans were no doubt fearing the worst, but it was a substitution of their own just four minutes later that would make the most telling impact.
United failed to heed the warning of Burke getting a weak shot away from inside the box and allowed the ball to be quickly recycled to the Scot so that he could smash a more powerful effort in off Axel Tuanzebe.
As he looked to mastermind a comeback, Solskjaer sacrificed Tuanzebe for Donny van de Beek, but the hosts were largely restricted to throwing crosses into the visiting box in the final minutes of the game.
And Sheffield United showed remarkable resolve to see off the bombardment, holding out for a victory that may even spark hopes of an unlikely late-season charge out of the relegation zone.
Substitute in, Donny van de Beek.
Substitute out, Axel Tuanzebe.
Substitute in, Luke Shaw.
Substitute out, Alex Telles.
Substitute in, Rhian Brewster.
Substitute out, David McGoldrick.
Assist given by John Lundstram.
Goal by Oliver Burke.
Substitute in, Oliver Burke.
Substitute out, Billy Sharp.
Substitute in, Edinson Cavani.
Substitute out, Mason Greenwood.
Assist given by Alex Telles.
Goal by Harry Maguire.
Substitute in, Jayden Bogle.
Substitute out, Kean Bryan.
Yellow card for Axel Tuanzebe.
Yellow card for John Lundstram.
Assist given by John Fleck.
Goal by Kean Bryan.