AC Milan's title hopes took an almost fatal blow on Sunday evening as they were beaten 1-0 at home by Napoli.
A second-half goal from Matteo Politano proved to be the difference at San Siro as Milan now fall nine points behind league leaders Inter.
The first half was a reasonably tight affair, with no clear-cut chances for either side.
Piotr Zielinski forced a save out of Gianluigi Donnarumma and also fired wide, while Rafael Leao was wasteful down the other end.
But it was Napoli who broke the deadlock just four minutes into the second half as Piotr Zielinski carved open the Milan defence and Politano slotted home with his weaker right foot.
There were chances for both sides after Politano's goal as Fabian Ruiz, Lorenzo Insigne and Victor Osimhen threatened for Napoli, while Leao and Ante Rebic had chances for Milan.
There was a late VAR review which could have given Milan a penalty for a foul on Theo Hernandez, but the referee opted against it after watching the pitchside monitor.
In injury time, Rebic was sent off for dissent to compound Milan's misery.