The Italy international fired home the first from the edge of the box after 72 minutes and added a second with a close-range overhead kick four minutes later to cancel out Krzysztof Piatek's first-half opener.
Rafael Leao was brought down in the area and the Polish striker stepped up to score from the penalty spot.
Hakan Calhanoglu saw an effort beaten away by goalkeeper Salvatore Sirigu as the visitors looked to double their lead, while Belotti should have equalised in first-half stoppage time with the goal at his mercy.
Piatek sent a shot inches wide, but Milan were pegged back when Belotti controlled a pass over the top and toyed with Mateo Musacchio before drilling the ball home.
The visitors felt there was a foul in the build-up and Pepe Reina, on the bench, was shown a red card for his protests.
The game was turned on its head shortly afterwards as Belotti grabbed his fourth goal of the season, acrobatically turning the ball in after Simone Zaza had seen a shot saved.
Franck Kessie blazed over the crossbar with the goal gaping in the third minute of stoppage time, with Sirigu somehow keeping out a Piatek header from point-blank range moments later as Torino held on.