The hosts threw away the chance to reclaim the Premier League summit as the Blades came through for their second win of the campaign
Manchester United defender Harry Maguire urged his team-mates to bounce back immediately after seeing them go down to Premier League basement boys Sheffield United on Wednesday.
The Blades powered to only their second league win of the season at Old Trafford in a shock 2-1 win.
Kean Bryan and Oliver Burke scored the visitors' goals to deny United the chance to return to the top of the Premier League table, after Manchester City went top on Tuesday with a 5-0 thrashing of West Brom.
Maguire had given his side brief hope with an equaliser on 64 minutes, and he acknowledged that United must return to form as soon as possible in order to stay in the race at the summit.
"It wasn't good enough, we didn't play to the level we have in recent weeks," the England centre-back admitted to BT Sport after the final whistle. "We gave them two goals, now it's time to stand up and be counted because it's easy when you are winning football matches - when you lose it is about how quickly you bounce back.
"We started the game in full control. We have to do more, we made it hard for ourselves, got ourselves back in it and you can't lose it from there.
"We knew at half time the next goal would be crucial, we had great belief we could do that again We weren't good enough tonight and didn't play to a level we expect from ourselves."
Manager Ole Gunnar Solskjaer shared his charge's frustration at dropping three crucial points, while also pointing out that United paid dearly for a handful of errors from referee Peter Bankes.
"Disappointed, we couldn't get to the heights of the last few months' football we played. Very disappointing, we couldn't find a solution to their very compact block and good defence," Solskjaer said. "Two wrong decisions, that's how it is, it's that kind of season, inconsistent and the referee missed those two.
"That little spark, that edge, we didn't have that extra creativity, imagination, the X factor we've had - it's happened, we look at it, agree it is not good enough and go again.
"We conceded a poor goal, lost the ball cheaply up the pitch, didn't get back in and tackle, didn't clear our lines and didn't get out to the ball quick enough and we were punished.
"There is no time to feel sorry for yourself because Saturday you go again, we have Arsenal, we have to forget this, learn from it and move on."