Manchester United suffered their worst defeat at the Etihad Stadium since 2004 as Manchester City ran riot.
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Sergio Aguero scored twice, and Yaya Toure and Samir Nasri added further goals, with Wayne Rooney grabbing a consolation in a 4-1 triumph for City manager Manuel Pellegrini in his first Manchester derby.
For United boss David Moyes it was a desperate day, an echo of a 5-1 defeat suffered by Sir Alex Ferguson at Maine Road in 1989 before his trophy-gathering had begun.
Ferguson missed this debacle, having flown to the United States on holiday on Friday. He would have found little to enjoy.
United's defending was awful and their midfield - including £27.5million new arrival Marouane Fellaini - ineffective, with Rooney's late effort doing little to paper over the cracks.
The loss was made more painful for the Red Devils by the knowledge of how bad they had been without their talisman, Robin van Persie, who was ruled out with a groin injury.
Van Persie's absence had increased a sense of foreboding among the United contingent, which, in fairness, their City counterparts also felt prior to kick-off. The tension was understandable given the early teething troubles both clubs had faced under their new management.
As it turned out, the visitors were right to fret.
Two days after Moyes had claimed Rooney had gone soft, he got the snaring England forward, ill at ease with the world, challenging every decision that went against him, of which there were a few.
By the time he took Vincent Kompany down from behind, referee Howard Webb had no alternative but to brandish a yellow card in Rooney's face, which did little to improve his mood.
Moyes was not happy on the touchline either, although by the time five minutes of the second half had elapsed the Scot had far more to occupy his mind than debatable refereeing calls.
With his team staring down the barrel of a possible rout even worse than the 6-1 hammering handed out to a team reduced to 10 men at Old Trafford in October 2011, Moyes was facing a crisis.
There was little excuse either.
Apart from a crisp opening 10 minutes, United were comprehensively outplayed by their neighbours, who made them pay for a sterile midfield display and truly awful defending.
One-time United target Samir Nasri was having one of his good days.
And when the Frenchman held the ball up intelligently on the side of the area and waited for Aleksandar Kolarov to charge forward on the overlap, Antonio Valencia failed to track him.
The Serbian's cross was perfect for Aguero, whose first time finish gave David de Gea no chance for the 16th-minute opener.
It was the third game in five Aguero had found the net against United. He was not done - and neither were City.
With Rio Ferdinand and Nemanja Vidic picked to start alongside each other for the third time in a week, for the first time since 2010, the veteran pair found themselves facing the impossible task of stemming a tide of attacks with their cover disintegrating.
When Alvaro Negredo climbed highest to reach Nasri's corner in the final minute of the opening period, Toure drifted away from Fellaini and touched the ball home with his knee from barely a yard.
It left Moyes needing to deliver some kind of half-time wake-up call.
But if the Scot thought about producing a hairdryer blast from the Sir Alex Ferguson school of management, he forgot to plug it in.
For those first five minutes after the re-start brought two more City goals.
And yet again, United's defenders were staring at themselves wondering where everyone had gone.
Kolarov's pass sent Negredo to the byline and his chip to the far post provided Aguero with the easiest of finishes as Patrice Evra and Vidic were again caught out of position.
Then, on City's next attack, after United had lost possession deep inside their opponents' half, Navas drove down the right to the byline before crossing to the far post, where Nasri supplied the first-time finish.
Immediately minds wandered back to United's Old Trafford nightmare of two years ago.
Yet the more obvious comparison was that dismal day at Maine Road nearly a quarter of a century ago, before Ferguson had even won a trophy.
That result is now just a footnote in United history.
For this to be the same for Moyes, the response will have to be pretty special.
Rooney did pull one back near the end, his strike making him the all-time leading scorer in Manchester derby games with 11 goals, although by then City had eased off.
Home fans singing "There's only one David Moyes" and "Sacked in the morning" underlined the new order in Manchester now.