Demolition derby: Manchester United get revenge on City rivals
Manchester United 4-2 Manchester City
Before his first defeat in a Manchester derby, Manuel Pellegrini admitted that in the space of a month Manchester City had "thrown our season in the garbage".
As the final whistle went it was time to sift through the trash and examine what, if anything, might be salvaged for next season.
This was their fourth defeat in five matches and, although losing at Old Trafford should not logically carry the embarrassment of defeats at Turf Moor or Selhurst Park, it will have hurt more.
Ever since Roberto Mancini's side put six past Sir Alex Ferguson's stunned team in October 2011, the colour of Manchester's football has usually been blue - and City had won the previous four derbies. This was quite a payback.
Pellegrini was assailed from every corner of Old Trafford by chants that he would be sacked in the morning. You would hope the achievement of steering City to the Premier League title last season would have earned a decent and talented man more than 11 months.
However, you could have said the same of Carlo Ancelotti before he was fired after he delivered the Double to Chelsea in 2010. The coming weeks will test how vicious City want to be.
It is, however, surely the beginning of the end of the praetorian guard Mancini assembled around him. The team Pellegrini sent out was essentially the one that had dominated this fixture for the past four seasons. Men like Yaya Toure, Vincent Kompany, Pablo Zabaleta and David Silva; men who deserve to be placed alongside the Bells and the Summerbees in City's pantheon.
For all except Silva, whose beautiful touch set up the first goal of an extraordinary afternoon, their time may be coming to an end.
For the Manchester United of Louis van Gaal, this may just be the beginning. After overcoming Tottenham and Liverpool, this was United's third important win.
United went a goal behind before relentlessly punishing their opponents with a series of superbly timed counter-attacks. Ashley Young, who scored the first and created the second for Marouane Fellaini, said that once they went ahead nobody felt they would lose.
City began the match with some fast, relentless attacks that climaxed with a couple of superbly weighted passes between James Milner and Silva, a quick low cross and the sight of Sergio Aguero driving home his first goal for two months.
Those tactics had triggered a wholesale collapse of the side managed by David Moyes but this is a rather more resilient Manchester United and within 19 minutes they were ahead.
Van Gaal's replacement of Moyes should have marked the end of the road for both Young and Fellaini. The latter had been mocked as a leaden-footed makeweight brought in by Moyes because he had run out of options in the transfer market.
Young was not only an embarrassment with a reputation as a diver, he had seen the club spend nearly £60m on Angel di Maria, who played in his position.
The game was 13 minutes old and the rain was crashing down when City demonstrated why they will not be champions of England for very much longer.
The slide began when an error from Phil Jones sent Aguero running through on goal. David de Gea dashed out to launch the ball to safety but it proved considerably more than an aimless punt. Fellaini headed it down and Ander Herrera sent over a low cross that was met by both Young and Gael Clichy. It rebounded off the defender's back and was turned into the net by Young.
Soon after, a neat interplay between Young and Daley Blind produced a cross that went beyond Clichy and was headed powerfully home by Fellaini at the far post.
City were losing their grip and losing control. A reckless tackle from Kompany sent Blind flying for a yellow rather than red card. The damage, however, was done. The City captain injured himself in the tackle and did not reappear after the interval.
If United had turned the tide in the first half, the second was a full blown flood towards the Stretford End. Wayne Rooney, who had been a strangely peripheral figure, came into his own.
Toure was pushed further back and for the third goal was accused of a "dereliction of duty" by Gary Neville for failing to protect his back four as Juan Mata was played through.
The Spaniard appeared to have delayed his shot too long but it was driven perfectly through Joe Hart's legs.
For City the game was up and, when Chris Smalling headed the fourth, they will have longed for it to finish. There was still time for Aguero to clip home his 100th City goal and it's hard to imagine an emptier milestone.