AS Roma's record-breaking run of away wins ended after their veteran midfielder Daniele De Rossi gave away a needless penalty and was sent off in a 1-1 draw at Genoa while big-spending AC Milan were held 0-0 at home by Torino.
Fiorentina converted a 93rd minute penalty, awarded with the help of VAR, to draw 1-1 at Lazio while champions Juventus cantered to a 3-0 win at home to lowly Crotone with second-half goals from Mario Mandzukic, Mattia De Sciglio and Medhi Benatia.
Napoli's win was their 12th in 14 Serie A games and left them top of Serie A on 38 points, two ahead of Inter Milan, also unbeaten, who led for less than 24 hours after a 3-1 win at Cagliari on Saturday.
Juventus, who visit Napoli on Friday, are third with 34 and Roma fourth with 31. Milan, in seventh on 20 points, failed to score for their fourth successive home league match.
Midfielder Jorginho scored Napoli's winner in the 33rd minute, snapping up the rebound after his own penalty was saved by Simone Scuffet, to hand Massimo Oddo a losing debut as Udinese coach.
Sarri said it was the sort of game that his team might well have lost last season and felt it proved they had learnt to win even when playing badly.
"Last year, in a scrappy game like today's we would have been in trouble," he said. "The improvement we have made this season is to win ugly games and that allows us to get the results we need even when we don't play particularly well.
"The pitch wasn't worthy of a top flight game. It's a reflection of Italian football."
Roma were leading 1-0 in a bad-tempered match when De Rossi was involved in an off-the-ball pushing match with Genoa forward Gianluca Lapadula at a corner and slapped him in the face.
After consulting the video replay system (VAR), the referee awarded a penalty which Lapadula converted in the 70th minute and the 34-year-old De Rossi was sent off. He later apologised for the incident.
Roma, who had won their previous 12 away games stretching back to February, had gone ahead 11 minutes earlier when Stephan El Shaarawy volleyed home Alessandro Florenzi's cross.
Defender Stefan de Vrij headed fifth-placed Lazio (29 points) ahead in the 25th minute at the Stadio Olimpico and they led until deep into stoppage time when Lazio substitute Felipe Caicedo, who had just come in, tackled German Pezzella.
The move continued but when the ball went out of play, the referee consulted the VAR and awarded a penalty for a Caicedo foul amid angry Lazio protests. Khouma Babacar converted to give eleventh-placed Fiorentina a point.
Juventus took 52 minutes to break down Crotone when Mandzukic headed in Andrea Barzagli's cross.
De Sciglio added the second with a long-range effort on the hour, the 25-year-old fullback's first-ever professional goal, before Benatia tapped in the third following a corner.
Milan coach Vincenzo Montella said his team did everything but score.
"We controlled the game, we conceded only a shot in the 85th minute," he said. "The team created a lot, increased the pace, we made mistakes, but we had (Torino goalkeeper) Salvatore Sirigu against us who did well."
(Writing by Brian Homewood in Berne; Editing by Clare Fallon, Ken Ferris and Ian Chadband)
