The Rossoneri got revived on a game they went behind through an acrobatic Rafael Leao bicycle kick and Olivier Giroud header.
With this win, they have now kept their hope of qualifying for the knockout stage alive.
The Rossoneri headed into the match with two points and zero goals in three Champions League ties. They also come into the clash following back-to-back 1-0 Serie A defeats.
The Milan ultras showed their readiness for the clash as they prepared thousands of fake banknotes with his face on to throw at Gianluigi Donnarumma on his first return as an opponent since the free transfer in 2021.
The first chance of the tie fell to Rafael Leao, whose snapshot was straight at Donnarumma. The Portuguese then skipped past Achraf Hakimi to set up Loftus-Cheek, who ballooned over from just inside the area.
PSG later opened the scoring through a corner. Marquinhos flicked on a corner kick to the back post, where former Inter defender Milan Skriniar was left unmarked. The defender made no mistake for a crouching header.
It was the turn of Yunus Musah to utilize an opportunity but the US midfielder’s shot was weak, having got the ball through a Davide Calabria pull-back.
Milan finally got their first goal of the tournament moments later through Leao. The attacker began the movement from the middle of the pack and spread it down the left for Olivier Giroud, whose angled drive was parried at the near post into the path of Leao to score with an acrobatic bicycle kick from six yards.
Mike Maignan was called into action as he ran out of lines to deny Kylian Mbappé after the offside trap failed. Then, the Ballon d’Or winner prodded wide in a similar situation.
As it became end-to-end stuff with both sides looking for a winner, Milan finally turned it around with a towering header from Giroud.
Leao slid in to meet a Christian Pulisic cross and couldn’t get there, but Theo Hernandez kept it in play. The French defender then whipped it in from the left for the towering Giroud header.