There were plenty of talking points from a dramatic night in Milan, which saw two players sent off and play suspended by referee Gianluca Rocchi shortly after half-time.
The Tuscan official used new league rules to halt play while a stadium announcement was issued to a section of Roma fans, who were allegedly directing abuse at several Milan players.
Sulley Muntari had earlier fallen foul of Rocchi at the end of the first half, earning a bizarre red card for dissent, and despite having an extra man Roma failed to find a winner before losing captain Francesco Totti for his elbow on former team-mate Philippe Mexes.
The Rossoneri must now wait until the final day of the Serie A campaign to match or better fourth-placed Fiorentina's result, while Roma's only hope of a foray into Europe rests on success in the Coppa Italia final.
Marquinho set the tone of the game in the third minute with a shot which Christian Abbiati did well to turn behind for a corner.
The Brazilian was dangerous again five minutes later with a shot on the turn which was too close to Abbiati to cause the Milan goalkeeper any problems.
Roma were preventing Milan from getting their game going, yet a well-drilled Rossoneri defence was keeping the visiting frontline at a safe enough distance from their goal.
A long-range effort from Totti blazed wide before he forced Abbiati into a diving save after 30 minutes.
The game was lively and boiled over just before half-time when Mario Balotelli was shown a yellow card for an innocuous foul.
Muntari protested and was shown the yellow card by Rocchi, but that was not enough to silence the Milan midfielder, who talked himself into another yellow card which he physically prevented Rocchi from showing him until his team-mates separated him from the official, who produced the red card.
The tension boiled over in the stands, too, prompting Rocchi to halt play for several minutes at the start of the second half amid unsavoury taunts emanating from a section of Roma fans.
Despite being a man down, Milan did not sit back and defend.
Balotelli tested Bogdan Lobont with a powerful direct free-kick which the Romanian goalkeeper collected at the second attempt.
Allegri introduced Giampaolo Pazzini and Robinho to further strengthen his side's attack, but they still suffered in defence with Erik Lamela unfortunate not to earn a penalty when Kevin Constant appeared to trip him inside the penalty area.
Balotelli's dipping free-kick just cleared the crossbar before Dodo was denied by Abbiati in a grandstand finish which did not herald a goal, but did bring a second dismissal.
Totti lashed out with his elbow at Mexes to earn a straight red card from Rocchi in the third minute of six minutes of time added on.