Roma put five points between themselves and AC Milan but the gulf between the two appeared much greater as the capital club ran out comfortable winners at the Stadio Olimpico.
Nicolas Burdisso got the ball rolling in the 13th minute with Pablo Osvaldo adding a second 10 minutes later. A brace from Erik Lamela finished Milan off, although Giampaolo Pazzini and Bojan Krkic scored late consolations after Marquinho was sent off for the hosts.
The determination with which Burdisso rose to head Roma in front in the 13th minute was suggestive of what was to come at the Olimpico.
It could have been different had Mauro Goicoechea not made a fine one-armed save to block Stephan El Shaarawy's route to goal four minutes later.
In the 23rd minute, Francesco Totti, who was unfortunate not to get a goal for his efforts too, set up Osvaldo with a textbook cross from the left which received a textbook finish with the Italy international's header going in off the far post.
Lamela got in on the act on the half hour mark, and peeled away to thank Daniele De Rossi for the pass which set up his ninth goal of the season. Totti pulled his best chance wide in the 50th minute as Osvaldo returned the first-half favour.
On the hour mark, Federico Balzaretti set up Lamela to head in his second and Roma's fourth as the home team dominated proceedings.
Kevin-Prince Boateng missed two chances to reduce the arrears in the 71st minute when his first shot was saved and his second hit the post.
Marquinhos was then shown a particularly harsh red card when he blocked El Shaarawy's route to goal with his arm.
Roma's win was never in doubt, but a team coached by Zdenek Zeman rarely keeps a clean sheet and the referee helped maintain that statistic by awarding a penalty when Pazzini saw Goicoechea's outstretched arm and went to ground.
Pazzini scored from the spot before Krkic added an instant second in the 88th minute, but they were unable to mask a dominant performance from Roma, who form part of six clubs who are now pulling away at the top.