Champions Inter claimed derby honours by hammering city rivals Milan 4-0 after Gennaro Gattuso was sent off in the first half last night.
Milan, and Gattuso in particular, self-destructed in spectacular fashion during a 10-minute first-half period in a match that suggests the loss of Kaka to Real Madrid has hit the red and black half of the city harder than they thought.
Thiago Motta scored his first goal for Inter and fellow new-recruit from Genoa Diego Milito added a penalty before full-back Maicon's strike had all but ended the contest by half-time.
Dejan Stankovic's second-half rocket put the gloss on an accomplished performance as coach Leonardo suffered a miserable first derby in charge of Milan.
Inter coach Jose Mourinho gave a debut to Wesley Sneijder following his move from Real.
The Dutchman showed his worth on six minutes, testing Milan goalkeeper Marco Storari with a curling effort from outside the box.
On 13 minutes Ronaldinho should have done better when teed up by Pato but after skying his shot miles off target and falling over in the process, the Brazilian tried claiming a penalty despite there being no contact from Stankovic.
Milan looked lively at that time but the first goal on 29 minutes changed everything.
It came from a sweeping team move on the edge of the Milan box as Motta fed Samuel Eto'o, who shifted the ball on to Milito before the Argentine played the ball behind the backline where Motta, who had continued his forward run curled a shot beyond Storari.
Six minutes later and Milan fell to pieces.
From a Milan free-kick, Inter broke at pace with Maicon lumping a long ball down the line for Eto'o to chase. The Cameroon forward skinned Gattuso who slung his arm around the Inter man's neck and hauled him down inside the box for a clear professional foul.
Inexplicably the referee only showed Gattuso a yellow card but Milito exacted adequate punishment by smashing his penalty home, straight down the middle.
Captain Gattuso had already signalled to the bench that he wanted to come off before the goal but his attempts to leave the field were hampered as substitute Clarence Seedorf wasn't ready.
Play continued and on 40 minutes Gattuso hacked down Sneijder, earning a second yellow before Seedorf had a chance to enter the fray.
Gattuso was irate and blasted his bench as he trudged off, leaving his team a man down.
To add insult to injury, Maicon scored a third on the stroke of half-time after a one-two with Milito as Flamini once again failed to track a forward run.
Stankovic's howitzer from 25 metres, halfway through the second period, was the final nail in Milan's coffin but tellingly, the nominal hosts at the San Siro had a hand in their own downfall as Andrea Pirlo failed to close down the Serbian, giving him time and space to pick his spot.