Coach Maurizio Sarri was sent off as Napoli wasted a chance to return to the top of Serie A when they were held 1-1 at home by AC Milan in a tense encounter.
The hosts, 4-0 winners at San Siro earlier in the campaign, went ahead in the 39th minute when Lorenzo Insigne's 25-metre effort took a wicked deflection off Ignazio Abate and wrong-footed goalkeeper Gianluigi Donnarumma.
Milan levelled five minutes later with their first shot on target, the unmarked Giacomo Bonaventura turning the ball in at the far post after it was unwittingly headed into his path by home defender Kalidou Koulibaly.
The home side dominated the second half but became edgy as they struggled to score a second goal, with Sarri being dismissed for persistent dissent.
Napoli, chasing their first league title since 1990, have 57 points from 26 games, one behind Juventus who drew 0-0 at Bologna on Friday.
Dries Mertens went closest for Napoli in the second half when he turned the ball against the foot of the post while team mate Omar El Kaddouri forced a point-blank save from Donnarumma with a snap-shot.
Milan almost ended Napoli's unbeaten home league record late on when Keisuke Honda's powerful low drive was turned around the post by goalkeeper Pepe Reina.
