AC Milan needed an injury time penalty save from Gianluigi Donnarumma to see off Torino 3-2 in Vincenzo Montella's first Serie A game at the helm after Carlos Bacca's perfect hat-trick apparently had them coasting to victory.
Former Sampdoria coach Montella has identified a Europa League place as Milan's target for the coming season, having missed out on continental competition all together last term, and their winning start here was down to Bacca's clinical goals and Donnarumma's last-gasp heroics penalty
It meant heartbreak for Andrea Belotti, who scored an earlier equaliser, and former Milan boss Sinisa Mihajlovic on his return to San Siro.
Under Mihajlovic, the seven-time European champions lost to Fiorentina on the opening day last term - one of four defeats in their first seven games - and he was controversially sacked by the club in April.
But a header, a left-footed half-volley and a right-footed penalty from Bacca made sure Montella would not endure a similarly disappointing Milan bow.
He also owed thanks to 17-year-old goalkeeper Donnarumma for denying the unfortunate Belotti. A frantic period of stoppage time saw Daniele Baselli net and Gabriel Paletta collect a second booking for pulling Belotti's shirt in the area.
Meanwhile, Mihajlovic was also involved in a pre-match confrontation with Milan's back-up goalkeeper Diego Lopez before the visitors fell to yet another San Siro defeat, having not beaten Milan in Serie A on this ground since 1985.
The hosts were aided by the absence of Torino's wantaway defender Nikola Maksimovic, and Milan forward M'Baye Niang was heavily involved in the game's early action.
Denied a first opportunity by debutant Luca Rossettini's fine interception, Niang then shot straight at Daniele Padelli, before thundering a volley into the side-netting from Bacca's smart centre.
The creation of a genuine chance settled the nervy San Siro crowd a little, but Adem Ljajic instantly responded with a mazy run, dragging his eventual shot wide.
Torino's former Roma and Inter midfielder was soon withdrawn through injury, though, despite battling on after a challenge with Alessio Romagnoli, and Milan renewed their attacking efforts.
Ignazio Abate's pace troubled Cristiano Molinaro throughout the half and he finally punished the experienced full-back in the 37th minute.
Racing on to a lofted pass in behind, the Italy international crossed for Bacca to nod a stooping header into the net.
However, just three minutes after the break, Torino were level.
Molinaro showed his own prowess at the other end with a glorious delivery towards Belotti, who gained a yard on Romagnoli to flick beyond Donnarumma.
Parity did not last long, with Bacca again prolific when given an opening. Niang crossed, and the Colombian had space to control and hammer a low finish into the corner.
Maxi Lopez was introduced for Torino and drilled wide, but a clumsy foul on Giacomo Bonaventura granted Bacca a hat-trick opportunity from 12 yards. He gladly obliged, hammering high down the centre of the goal.
Bacca could even have had a fourth, running clear but finding his path blocked by the smothering Padelli - a botched opportunity he would remarkably almost come to regret.
Substitute Andrea Bertolacci suffered and injury shortly after coming on for Milan and their afternoon almost unravelled entirely during stoppage time.
First, Baselli battled through the Milan backline to slip a cool finish under Donnarumma, but the teenager was ultimately the hero as he sprung to his left to keep out Belotti's spot kick.