Mario Balotelli was booked within 30 seconds of coming off the bench in the first half to replace the injured Giampaolo Pazzini, who had just given Milan the lead.
Balotelli then latched onto Cristian Zapata's pass to fire home the second goal with an hour played.
It was Balotelli's fifth goal in as many matches since joining Milan. The former City forward was making his first appearance since the Milan derby two weeks ago.
Former Arsenal midfielder Mathieu Flamini was also booked for diving as he tried to win a penalty in the second half.
Milan came under extreme pressure after Kevin Constant was sent off in the 65th minute for lashing out at Genoa defender Cesare Bovo, but their defence held firm as they strengthened their grip on third place in Serie A ahead of Tuesday's Champions League clash with Barcelona.
Milan now have 51 points, two behind second-placed Napoli and four ahead of Inter Milan and Lazio.
- Daily Mail
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