AC Milan missed out on the chance to move into second in the Serie A standings when they lost 4-2 at mid-table Monza on Sunday after being reduced to 10 men early in the second half.
Milan remained third in the standings on 52 points, two adrift of second-placed Juventus and 11 behind leaders Inter Milan, who have a game in hand.
The Rossoneri, who beat Stade Rennais 3-0 at home in the Europa League in midweek and travel to France for the second leg on Thursday, suffered their first league loss in more than two months to end their unbeaten run of nine games.
Matteo Pessina and Dany Mota put Monza ahead in the first half before substitutes Olivier Giroud and Christian Pulisic pulled Milan level in the second. Warren Bondo and Lorenzo Colombo secured the hosts all three points with a goal apiece in the dying minutes.
Milan went down to 10 men in the 52nd minute when Luka Jovic was sent off for violent conduct against Monza captain Pessina, with the referee overturning his original decision to just book the Serbia striker after consulting the VAR screen.
"We made mistakes that ruined the match. When you concede four goals it feels wrong to say our first half-hour was good, but that is true," Milan coach Stefano Pioli told DAZN.
"Going a man down made it even more difficult. After equalizing we should've been sharper to defend better. The team felt confident and wanted to go on to win."
With Giroud, Pulisic and Rafael Leao starting on the bench, Milan had early chances through Jovic and Theo Hernandez before a shot by Samuel Chukwueze was denied by Monza goalkeeper Michele Di Gregorio.
Pessina gave Monza the lead from the spot just before the break, sending Milan keeper Mike Maignan the wrong way after the penalty was awarded for a foul by Malick Thiaw, and Mota doubled the advantage for the hosts in first-half stoppage time.
Di Gregorio had to be substituted late in the first half after a clash of heads with defender Andrea Carboni.
Pulisic, Leao and Tijjani Reijnders all took to the field following halftime and Giroud joined minutes later but things got worse for Milan when they had Jovic sent off.
Giroud eventually pulled a goal back for the visitors with a shot from close range, netting a Pulisic headed pass in the 64th minute, and the American equalized in the 88th with a curled shot inside the far post.
But feisty Monza did not settle for a draw, with Bondo and Colombo sealing their historic first win and points over Milan in Serie A.
"These are serious errors; we all should've done better. It is a painful defeat but one that we must learn from," the Italian manager added.
"We stopped after a long unbeaten run in Serie A, third place is not solid yet and second place is also not far away."
