A total of five changes from their loss to Hellas Verona saw Gianluigi Buffon, Mattia De Sciglio, Aaron Ramsey, Blaise Matuidi and Paulo Dybala entering, while Davide Calabria was Milan's only change from the loss to Inter Milan on Sunday.
Milan came close to a second-minute opener when Hakan Calhanoglu created space to find Zlatan Ibrahimovic in the area, who headed over the top. Thereafter, a sustained bit of pressure from Juve brought Milan to a spot of bother as the Bianconeri probed and probed for the breakthrough.
Milan however quickly regained momentum at the midway point and a one-handed save from Buffon denied Calabria after the full-back found space outside the area for a smart attempt.
Juan Cuadrado gave Juve their first big opening nine minutes to the break as the Colombian brought Milan goalkeeper Gianluigi Donnarumma to a low save following a strong effort.
Milan finally went ahead inside the 61st minute as Ante Rebic, who netted in the Milan derby, volleyed home a cross from Samu Castillej, giving Buffon no chance whatsoever.
Juventus responded to their set back with the evening's first change two minutes later in Rodrigo Bentancur, who replaced Ramsey.
A strong late challenge from Theo Hernandez on Dybala gave the man in the middle no choice but to send the full-back for a shower on 71 minutes as he received a second yellow card.
Dybala was involved in the flurry of late chances when he fired wide from the near post following a decent move.
Juve levelled at the death through a penalty from Ronaldo after Calabria handled in the area, giving the visitors an away goal ahead of the return-leg in three weeks time.