Carlos Bacca scored a hat-trick but AC Milan needed an injury-time penalty save from teenage goalkeeper Gianluigi Donnarumma to secure a 3-2 win against Torino at San Siro.
Bacca bagged his first with a diving header to convert Ignazio Abate's cross after 38 minutes but three minutes into the second half Torino, managed by Sinisa Mihajlovic who was sacked by the Rossoneri last season, were level when Andrea Belotti headed home a Cristian Molinaro cross.
Bacca immediately restored the hosts' lead with a tidy piece of control and an assured finish after he was picked out inside the penalty area by M'Baye Niang.
The Colombia international completed his treble in the 62nd minute from the penalty spot, blasting his shot straight down the middle.
Milan looked home and hosed but there was still some late drama to come. Daniele Baselli pulled Torino within a goal in the first minute of injury time when he collected a loose ball 25 yards out and wriggled his way into the area before beating Donnarumma with a low shot.
Belotti was then brought down by Gabriel Paletta, who was subsequently sent off, and the referee awarded a penalty. Belotti took the spot-kick himself but his effort was dramatically palmed away by Donnarumma diving to his left.
The 17-year-old's save ensured Vincenzo Montella made a winning start in Serie A, having been appointed Milan manager in June.