Harry Maguire appeared to 'dummy' the ball instead of putting it out for a corner in a damning moment during Manchester City's second goal.
Kevin De Bruyne put his side in the lead, with Jadon Sancho cancelling out his strike.
But the Belgium ace restored Man City's lead six minutes later thanks to some woeful defending from the visitors, in particular Maguire who made a bizarre choice in the box.
After David De Gea saved Phil Foden's initial attempt, the ball came to the Manchester United defender who appeared to let the ball run through his legs.
From there, Bernardo Silva had a shot which was blocked, with De Bruyne coolly slotted home.
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Maguire's odd decision-making angered Man United fans, with his showing at the back sending social media into overdrive.
One tweeted: "Both goals were solely his fault."
A second wrote: "Legitimately think he attempted to kick, but missed. Not sure which is worse."
A third added: "Sell the man. I’m fed up of him, completely sums up why this club isn’t successful at the moment. Worst ever value for money signing."
Maguire's outing went from bad to worse when Riyad Mahrez struck an effort that hit the defender before hitting the back of the net.
Mahrez made it 4-1 late on following a VAR review.
Topics: Harry Maguire, Manchester United, Football
Nasir Jabbar