Ronaldo put the Rossoneri ahead after 40 minutes, but Inter battled back to score two second half goals, the first from Julio Ricardo Cruz, and the second from Ibrahimovic, to keep its unbeaten record in tact.

After qualifying for the quarterfinals of this season's Champions League during the past week, AC Milan went into the contest hoping to take another step towards qualifying for next year's competition. However, the loss leaves them six points behind both Lazio and Palermo for the final spot.

Inter crashed out of the Champions League after being held to a 0-0 draw against Valencia, but coach Roberto Mancini's side responded with a strong effort that led them to its second win this season over their city rivals.

AC Milan produced the early scoring chances with Andrea Pirlo threatening keeper Julio Cesar's net on a couple of occasions. Ibrahimovic should have been awarded a penalty kick after a half hour as he was brought down by defender Daniele Bonera. However, it was Ibrahimovic who drew the ire of the official as he was booked for diving.

It was a tough break for Inter, but the Nerazzuri then found themselves down a goal 10 minutes later. Former Inter striker Ronaldo, who spent five seasons with the club, took possession of the ball on right 35-yards from goal. He beat Maxwell with one touch and cut inside before driving a left-footed shot past keeper Nelson Dida and into the bottom corner.

Gennaro Gattuso had a great chance to double AC Milan's lead after the restart, but watched his shot slip narrowly past the far post. Less than one minute later, Inter leveled the match.

Cruz was brought on as a substitute and just 10 seconds after he stepped onto the pitch, he scored the equalizer. Ibrahimovic carried the ball down the right flank and crossed for Cruz but the cross was not pulled back far enough. Dida was able to get a touch on it but he could not bring it in, leaving the ball for Cruz to tap in and tie the game.

The duo then teamed up for the match-winner 15 minutes from time. This time it was Cruz who supplied the cross. He stripped AC Milan's Marek Jankulovski in his own end and slid a pass from the right to Ibrahimovic, who struck it first-time into the bottom corner past a diving Dida.

The goal was too much to overcome for the Rossoneri, who lost for the first time in the calendar year.

In other Serie A play on Sunday, Atalanta and Parma played to a 1-1 draw, as did Messina and Chievo. Empoli and Livorno shared the points in 2-2 fashion while Lazio moved into third place with a 3-2 triumph over Reggina. Palermo fell to fourth after being held 1-1 by Fiorentina, Ascoli moved out of the cellar with a 1-0 win against Siena, Torino blanked Catania 1-0 on a goal from Alessandro Rosina and Roma topped Udinese 3-1.