Giampaolo Pazzini scored the opener only to be then forced off through injury, but his replacement, Mario Balotelli, added a second before Kevin Constant saw red.
AC Milan maintained its fine form ahead of its Champions League showdown with Barcelona by strengthening their grip on third place in Serie A with a hard-fought 2-0 win over Genoa on Friday night.
The Rossoneri were nowhere near their best at the Luigi Ferraris, breaking the deadlock against the run of play through Giampaolo Pazzini 22 minutes in.
Massimiliano Allegri's men then survived three strong penalty appeals before bagging a crucial second goal through the returning Mario Balotelli on the hour mark. Kevin Constant saw red for violent conduct soon after but Milan held on to move to within two points of second-placed Napoli.