Alessandro Nesta and a Zlatan Ibrahimovic brace gave Milan an impressive 3-2 victory at the Olimpico that adds to Roma's crisis.
The Rossoneri were back on form with six wins from their last seven games in all competition, including three Serie A victories on the bounce. They gave Robinho his first start of the season and Alberto Aquilani faced his former club, even though fellow ex-Romanisti Antonio Cassano (bench) and Philippe Mexes (injured) missed out. Clarence Seedorf, Alexandre Pato and Gennaro Gattuso were among the absentees. Patience was running thin at Roma after a midweek defeat to Genoa, so Luis Enrique reshuffled his side again, as Miralem Pjanic shook off a knock to replace the injured Francesco Totti.
The last three League editions of this fixture ended in draws. As expected, before the opening whistle Milan assistant manager Mauro Tassotti shook Luis Enrique's hand, apologising for having broken his nose during the 1994 World Cup.
Marco Cassetti blasted wide of the near post, while Fabio Borini's turn and strike was charged down for a corner.
Mark Van Bommel needed a crucial intervention to stop David Pizarro tapping in a deflected Pjanic cross totally unmarked.
A not dissimilar move occurred at the other end when Jose Angel cleared a dangerous low pass across the six-yard box.
Zlatan Ibrahimovic put Milan in front after 17 minutes by beating his former Ajax teammate Maarten Stekelenburg. The Swede rose in front of both Juan and Nicolas Burdisso for a powerful header at the near post from Aquilani's cross.
Roma fought back, as Christian Abbiati flapped at a Cassetti cross. Robinho saw Stekelenburg off his line from a Roma corner and tried to audaciously lob from midfield, but it was off target.
The Giallorossi equalised from a set play, which has always been a weakness for Milan's defence. The corner from the left found defender Burdisso, who used his strength to get in front of Gianluca Zambrotta and power home the header from nine yards.
The situation did not last long, as moments later Alessandro Nesta restored Milan's lead. It was another corner from Robinho and the former Lazio man was allowed a free header from eight yards against the team he faced so many times in the Rome derby. Nesta had never previously scored against Roma, while his last goal was in January 2010.
Abbiati needed two attempts to get a Pizarro snapshot under control, but Roma lost Fabio Borini to a muscular problem as he stretched to reach a Jose Angel assist, making way for Bojan Krkic before half-time. The young Spaniard drilled wide, then set up Cassetti only for his first touch to let him down.
Antonio Nocerino was booked and will be suspended for the next Milan game with Catania.
Bojan had a great chance after good work from Osvaldo through the middle, but Abbiati and Zambrotta combined to send him wide and Nesta dived in with a crucial clearance from a yard.
Abbiati flew to palm a screamer of a long-range Pjanic free kick round the far post. From that corner, Burdisso's diving header was fingertipped out from under the bar after a tussle with Kevin-Prince Boateng.
Ibrahimovic was furious with Aquilani when totally unmarked and the midfielder's cross went wayward. Boateng limped heavily when leaving the field for Urby Emanuelson, but strangely he was shown a red card as he got to the bench, perhaps for something he said to the fourth official.
Juan also had an injury, while substitute Erik Lamela's daisy-cutter was deflected wide. From the corner Osvaldo got his head to it from point-blank range, forcing a splendid save from Abbiati.
Aquilani hit a rocket from distance that skimmed the upright and substitute Cassano skipped past Burdisso with some fantastic footwork only to blast the finish well wide.
Milan extended their advantage after a period of pressure. Again it was a corner played short for Cassano, then Aquilani chipped it back into the middle for an Ibrahimovic twisting header. However, replays suggest the Swede was marginally offside.
Ibrahimovic attempted his hat-trick by volleying Cassano's cross over at the back post. Cassano created another on the counter that Nocerino only had to tap in from a couple of yards, but the midfielder incredibly ballooned off target.
It still wasn't over, as Lamela's angled drive was only palmed away by Abbiati into the path of Bojan Krkic to pull a goal back, making it 3-2.
Milan Coach Massimiliano Allegri was sent off from the touchline for dissent, joining Boateng, in stoppages. There was panic in the Milan box, as crosses rained in and Abbiati flapped one off the head of Daniele De Rossi, another out of the six-yard box and eventually managed to smother at the near post.