The former Italy international struck the only goal of the game midway through the second half to lift the Zebrette ten points clear of the drop zone, and to within four points of the Rossoneri, who have now lost two in a row.
Clarence Seedorf's men could fall as much as nine points adrift of the top five this weekend following the 1-0 loss, putting them under increased pressure to reach the quarter-finals of the UEFA Champions League when they face Atletico Madrid on Tuesday night.
Milan need to overturn a 1-0 deficit in Spain if they are to continue in Europe.
There was encouragement from their performance against Juventus last weekend, if not from the result - a 2-0 defeat.
In the day's later match,
The Sicilians fell behind to Matias Vecino's 53rd-minute strike, but were unlucky not to take all three points once Gonzalo Bergessio headed in a Francesco Lodi free-kick soon after.
Catania built up a head of steam as Danilo Avelar was red-carded on 73 minutes, but Alexis Rolin's header against the crossbar was as close as they came to a win that would have lifted them out of the bottom three.