Substitute Luiz Adriano's last-gasp winner saw AC Milan edge past 10-man Sassuolo, ending a three-match winless run, as 16-year-old goalkeeper Gianluigi Donnarumma made his debut.
Carlos Bacca put the Rossoneri ahead from the penalty spot in the 31st minute after the being brought down by former Atalanta goalkeeper Andrea Consigli, who was sent off for the incident.
Sassuolo equalised before the hour-mark through Domenico Berardi's free-kick but, just as it looked set to head for a draw, Adriano came to the rescue, powerfully heading home to hand Milan a 2-1 victory that eases the pressure on coach Sinisa Mihajlovic.
The Rossoneri boss dropped veteran goalkeeper Diego Lopez from the starting line-up for this game, instead handing Donnarumma his debut, becoming the youngest keeper to start a Serie A game.
Donnarumma was called into action seven minutes in when he kept out Karim Laribi's 25-yard attempt, but disaster struck for Sassuolo shortly after when Bacca fell in the area after contact from Consigli.
The goalkeeper was handed his marching orders and Bacca struck home the spot-kick past substitute Gianluca Pegolo.
Sassuolo pulled level eight minutes after the re-start, with Donnarumma unable to get a touch on Berardi's powerful free-kick towards the far post.
But just when the visitors thought they had secured a point, Milan got the winner as Adriano rose highest to head a corner past Pegolo four minutes from time.