Manchester United suffered their worst defeat at the Etihad Stadium since 2004 as Manchester City ran riot.
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 Â£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.