Manchester City made 'The Theatre Of Dreams' a house of pain for Manchester United as they brutally demonstrated the gulf between a modern, upwardly mobile club and one in a state of disrepair.
Old Trafford's leaking roof, the result of a pre-match thunderstorm, was almost symbolic of the current condition of United as City - once airily dismissed as "the noisy neighbours" by Sir Alex Ferguson - brutally emphasised their vast superiority with a punishing performance to take a measure of control in the Premier League title race.
The facts of the matter are simple.
City's 2-0 victory margin barely scratches at how much better they were than United. It means they are now a point ahead of second-placed Liverpool and know three wins from their last three games will retain their title.
This was City's game in hand, identified as potentially their most hazardous assignment.
It was an assessment that leaned on history rather than logic, a judgement based on the United of old rather than this current band of misfits who, in a footballing context, cannot bear any semblance of comparison with Pep Guardiola's side.
Once the brilliant Bernardo Silva put City ahead in the 54th minute this game was over. Leroy Sane's goal was simply the confirmation. United looked like they wanted the game to end once when they went behind.
At the final whistle, Old Trafford was awash with vast red spaces created by empty seats while City's fans celebrated a win of great significance.
The most stark and harrowing aspect of a win Guardiola celebrated after much technical area agonising - crouching, kneeling, imploring, demanding - was the sheer measure of how far apart these two teams, two clubs, are.
Manager Ole Gunnar Solskjaer demanded a reaction from United's players after their 4-0 mauling at Everton on Sunday - he got one of sorts in that it was not as bad as the Goodison Park fiasco, but for him to claim the response was "great" was killing these players with kindness.
It is to be hoped Solskjaer was merely indulging in man-management to keep them going in the hunt for the top four against Chelsea on Sunday because if he seriously believed this was a great reaction it is an act of delusion.
There were other ominous signs and sounds.
Solskjaer's language was that of the plucky loser, talking about how the players "had a go".
In fact, it was the sort of language City managers used to use as a matter of routine after defeat by United in days gone by - before the balance of power shifted so emphatically. This will be the sixth successive season City have finished above United.
Marcus Rashford was off message - and correct - when he said: "We didn't play like Manchester United. It's not right. The bare minimum is to give all for the badge, the supporters, the club and yourself."
Solskjaer took United's players to the club's famous old training ground The Cliff in the build-up to this derby. Was it to connect them to the club's great history and successes? Judging by their lame performance, it was a nice try but lost on them.
He said: "We have to work harder and have a better attitude than anyone else."
Fine words, but the bottom line is Solskjaer needs better players and United need a better, more focused strategy to buy the right players because this is currently a mess.
United's team is springing more leaks than that Old Trafford roof, with some of the culprits the usual suspects and others coming late to the party.
Paul Pogba felt the ire of some supporters for his poor performance, summed up by losing a straight aerial challenge to the diminutive figure of Raheem Sterling. There was the difference.
It is actually hard to fathom how Pogba can seriously attract interest from the likes of Real Madrid when he regularly fails to make an impact. If he did leave, would he even be missed?
And then there is goalkeeper David de Gea.
It was another awful night for the Spain international, beaten at his near post by Silva and flimsy for Sane's second. A pattern is emerging after errors against Barcelona and Everton in the past seven days.
He and others are living off reputation and these are thorny problems for Solskjaer to solve. Romelu Lukaku struggled with basic control when he appeared as a substitute, while what can laughingly be described as Alexis Sanchez's "touch map" showed he had one in a 12-minute substitute appearance.
Contrast this with City, who coped consummately with the pressure of knowing only victory would do or the title initiative would switch firmly in Liverpool's favour.
Contrast goalkeeper Ederson's decisiveness - summed up by a brilliant and brave high-speed dash from goal to halt Rashford in the first half - to De Gea's uncertainty.
Contrast City's measured probing to United's increasing lumpen, unsophisticated approach.
In fact, contrast just about everything.
This title race, with two outstanding teams fighting it out, is nowhere near over and few would bet against a twist or two yet even as the finishing line comes in to sight. But this was mightily impressive from City.
City looked jaded and nervous in victory against Tottenham on Saturday after the anguish of their Champions League exit against Mauricio Pochettino's side, but here they looked re-energised, exemplified by the manner in which Sane came off the bench and threatened instantly.
Next stop is Burnley on Sunday, when victory is also likely to be the requirement after Liverpool face relegated Huddersfield Town at Anfield on Friday night.
Liverpool looked in the unlikely direction of old foes United for a favour in pursuit of their first title in 29 years. They looked in the wrong place.
United were not good enough to help them and City were too good to slip up.