Aaron Wan-Bissaka has made a name for himself in Manchester derbies with his one-on-one defending consistently shutting down Raheem Sterling, but his old foe's absence from the Manchester City line-up made for a very different afternoon.
Manchester United knew they were in for a tough fixture against Premier League leaders City but they played well in the first half, only to be undone by two instances of abysmal defending.
And in both instances, Wan-Bissaka could be apportioned a large amount of the blame.
On the first City goal the right-back should have done much better dealing with Bernardo Silva and blocked his cross into the box, which found Kevin De Bruyne - undermining his claim to be United's best out-and-out defender.
The second goal confirmed why Diogo Dalot was preferred to him in the early stages of Ralf Rangnick's tenure as interim manager.
His attempt to progress the ball up the field was weak and cut out easily by City who again attacked down the United right. Wan-Bissaka tucked into the box, but when the ball was deflected out by David de Gea he switched off.
This lapse in confrontation caused him to be drawn to the ball instead of realising the other danger around him and, though Harry Maguire was able to block Silva's follow-up from Foden's initial shot, De Bruyne was again free in the box to finish the chance.
This was the story of Wan-Bissaka's game. City sensed the weakness of the defender both in and out of possession and forced a lot of play down his side.
And when the play was directed down the other side, Wan-Bissaka didn't follow his man, leaving multiple players unmarked at the back post.
Luckily, City didn't take advantage of this, but they were still able to get another two thanks to Riyad Mahrez, with his first being a well-worked corner he clipped home on the half-volley via a deflection off Maguire when unmarked.
It came to a head in the 74th minute when Fred appeared to lose his temper with Wan-Bissaka.
Fred, seemingly sick of his defender losing possession and getting beaten down the right, began to clap and shout at Wan-Bissaka in an attempt to push him to do more, but it was too little too late.
In a fixture that has felt like 'his game' in recent years, Wan Bissaka looked like he was drowning and it highlighted the clear weakness in his game.
Rangnick will have taken note as the battle for a top-four place just got tougher, his earlier doubts about Wan-Bissaka proved to be worryingly on the money
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