A goal and three assists from Italy international Domenico Berardi piled on the misery for Milan as Sassuolo thrashed the Rossoneri 5-2 at San Siro.
Sassuolo took an early two-goal lead thanks to goals from Gregoire Defrel and Davide Frattesi prior to Olivier Giroud pulling one back for the hosts.
Berardi made it 3-1 after just 30 minutes before Armand Lauriente s penalty and Matheus Henrique s effort in the second half handed Milan their second chastening loss in a week after their 4-0 humbling at Lazio on Tuesday.
Divock Origi scored a consolation for Stefano Pioli s side, who are now six games without a win heading into next weekend s Milan derby, including four in Serie A as their title defence continues to falter.
4 AC Milan have conceded at least 4 goals in 2 Serie A matches in a row for the first time in their history. Hit.
— OptaPaolo (@OptaPaolo)
A VAR review denied Giroud an eighth-minute opener and, to make matters significantly worse, Milan found themselves two down inside 22 minutes.
Berardi squared for Defrel to tap in the opener before the same man fed Frattesi, who fired past Ciprian Tatarusanu at his near post after great work in the area.
Milan provided a swift response when Giroud expertly headed Davide Calabria s cross into the far corner in the 25th minute.
But the two-goal lead was restored on the half-hour mark when Berardi flicked a near-post header past Tatarusanu from a corner.
Milan s hopes of a second-half comeback were doused almost immediately as Lauriente was brought down in the penalty area by Calabria after 33 seconds of the restart, allowing the Frenchman to make it 4-1 from the spot, meaning Milan had conceded at least four goals in back-to-back Serie A games for the first time in their history.
Ante Rebic had a goal ruled out for offside before Henrique fired in a fifth with just over 10 minutes remaining, with Origi s curling strike into the top corner doing little to lift the gloom among the home fans.
What does it mean? Milan in crisis after another heavy defeat
If the performance at Lazio was concerning, this one will have set off all kinds of alarm bells for the holders.
While Milan have been on a bad run, Sassuolo had not won a competitive game in eight attempts prior to this (D2 L6) and had not won away from home since September.
They found this game surprisingly easy though as they tore through Pioli s men time and again, having nine shots in all and hitting the target seven times.
Berardi targets Rossoneri again
Berardi terrorised the hosts on Sunday, and not for the first time.
The 28-year-old now has 18 goal involvements against Milan in his career (11 goals, seven assists).
Leaky Milan cannot find a win
Milan have now failed to win each of their past six games (D2 L4), last going as long without a victory in April 2018 under Gennaro Gattuso.
This was also the first time they have conceded at least five goals in a Serie A home match since April 1997 (lost 6-1 to Juventus).
Key Opta Facts:
Milan have conceded at least five goals in a Serie A home match for the first time since April 6, 1997 (6-1 defeat to Juventus).
The Rossoneri have conceded 18 goals in seven games since the start of 2023, more than any other side in the top-five European Leagues in this calendar year across all competitions.
What s next?
Milan face Inter at San Siro next Sunday while Sassuolo host Atalanta on Saturday.