The on-loan Liverpool striker converted a first-half spot kick to give Sinisa Mihajlovic's side a narrow lead ahead of the second leg at San Siro in early March.
Mario Balotelli marked his first start since September with a goal as AC Milan secured a 1-0 win over Alessandria in the first leg of their Coppa Italia semifinal.
The Liverpool loanee, recently returned from a groin injury, opened the scoring from the spot to help Sinisa Mihajlovic's side take charge of the tie in Turin.
Milan started with Balotelli alongside Luiz Adriano, who seemingly saw a move to China fall through this week, but chances were few and far between for either side in a scrappy contest.