Kevin De Bruyne went off to a standing ovation and a huge hug from Pep Guardiola.
This was right up there with one of De Bruyne's best performances, single-handedly destroying Manchester United at the Etihad.
De Bruyne was substituted in the 80th minute, his job done with two goals and an assist for Riyad Mahrez as Manchester City sent out a clear message of intent in the title race while they embarrassed United in the process.
It was actually quite an even first half, hard fought and a tough derby contest. But towards the end of the second half, the gap between the two Manchester rivals had never felt bigger.
City ended up toying with United, the fans going through their repertoire of songs in delight. Even the prawn sandwich brigade in the Tunnel Club were doing the Poznan while the away end just sat in stunned silence and disbelief.
Guardiola’s men are six points clear again at the top - admittedly having played a game more than Liverpool - but if this was supposed to be a test of their mettle there are no signs they are about to crack.
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The bigger worry for United was the absolute shambles in defence, Harry Maguire is suffering badly and Ralf Rangnick will be even more concerned at the way his players just waved the white flag when they went 3-1 down.
It was shameful.
United looked dangerous in the first half, woeful after half time and that was partly down to City’s dominance but partly down to their own failings. Now their place in the top four looks in danger.
In contrast, City look unstoppable. Any notion that United might do Liverpool a favour was just pure fantasy. They are nowhere near good enough. This was a throwback to the dog days of Ole Gunnar Solskjaer’s reign.
Back in November, Guardiola won 2-0 at Old Trafford where the scoreline did not reflect City’s dominance. This time, the scoreline underlined an old school thrashing.
Every time De Bruyne got the ball at his feet, he looked unstoppable, galloping from midfield to attack.
He was a joy to watch. City’s first came after five minutes after Mahrez’s low cross found De Bruyne, United’s defence was slow to react and the Belgium midfielder swept home.
City were not in top gear while United looked dangerous on the counter. It was a strange formation, no Cristiano Ronaldo, but it meant they all took it in turns to get forward. Paul Pogba played in Jadon Sancho, the United winger cut inside and curled into the far corner.
City regained the lead after 28 minutes. Anthony Elanga played United into trouble, Phil Foden was denied by David de Gea, Bernardo Silva had a follow-up shot blocked and there was De Bruyne to power home amid United defensive chaos.
But the second half was a different story. City took complete control - and United had no answer. The third City goal was a peach.
De Bruyne’s corner picked out Mahrez on the edge of the box and his sweetly struck shot deflected off Maguire and past de Gea.
De Gea saved it from being an even bigger mauling with some super saves. Then in the 90th minute, Mahrez raced through to score a fourth - his 21st in all competitions this season - and eventually it stood after a lengthy VAR check showed Alex Telles’ boot played him onside.
That just rubbed salt into United wounds. And gave City even more reason to celebrate.
