If you're Jose Mourinho, it doesn't get much worse than losing to Pep Guardiola.
In fact, the only thing that could possibly make it worse would be if Manchester City's victory had been masterminded by a player whom Mourinho sold while at Chelsea because he didn't think he was good enough for the Premier League.
Unsurprisingly, it was Kevin de Bruyne who bossed the Manchester derby, duly coming back to haunt the Special One with a sensational performance.
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The Belgian slipped past Daley Blind, who was then caught ball-watching for the first goal, before setting up the second with some fine work in the box.
De Bruyne once again teased past Luke Shaw and Blind to hit the post, Kelechi Iheanacho finding the back of the net from the rebound.
"Manchester United like mannequins" was Gary Neville's verdict on the hosts' shoddy first-half defending, but it was City's playmaker who was at the heart of their brilliant attacking play.
De Bruyne "unreal"
The 25-year-old was pretty anonymous in last season's corresponding fixture, but that definitely wasn't the case this time around - and as always, Twitter exploded with fans hyping over De Bruyne's performance.
In the 75th minute, he could have made it 3-1, hitting the woodwork again, with the ball rolling agonisingly across the goal line. It's fair to say he'd already done more than enough, though, easily making up for the absence of the suspended Sergio Aguero.
The only concern for City will be that he may have picked up a knock late on, looking as though he wanted to come off in the final minutes.
Is Kevin de Bruyne the best playmaker in the Premier League? Have your say in the comments.