Empoli twice fought back to earn a 2-2 draw with AC Milan at the Castellani.
The Rossoneri came into the match on the back of a 2-0 home win over Fiorentina and reaching the semifinals of the Coppa Italia.
Sinisa Mihajlovic's men looked set to continue their recent improvement when they went ahead through Carlos Bacca after just eight minutes, the Colombia forward beating the offside trap to latch onto a long through ball and slot past goalkeeper Lukasz Skorupski.
Empoli, who had lost just once in the past eight Serie A matches, regrouped and Massimo Maccarone's glancing header was ruled out for offside.
But the hosts were level on 32 minutes when Poland midfielder Piotr Zielinski was set clear down the right and he beat teenager Gianluigi Donnarumma in the AC Milan goal.
Milan went 2-1 up at the start of the second half following a fortuitous goal from Giacomo Bonaventura.
A clearance from Empoli defender Lorenzo Tonelli struck Milan forward M'Baye Niang in the head, and the ball dropped at the far post for midfielder Bonaventura, who slotted past Skorupski.
Empoli again had to force their way back into the match and were rewarded after 61 minutes when a free-kick from Manuel Pucciarelli was pushed away by Donnarumma and Maccarone lashed in the rebound.
Both sides had chances to win the match during the closing stages as first Zielinski sent his shot over, before Mario Balotelli and Bacca then both failed to make the most of their late opportunities.