Napoli will go into the delayed winter break top of Serie A after beating relegation-threatened Hellas Verona 2-0 on Saturday.
Kalidou Koulibaly and Jose Callejon scored as Napoli stayed one point clear of second-place Juventus, which won 1-0 at Cagliari in the late game.
Juventus has won the title in each of the last six seasons, while Napoli is bidding for its first since 1990.
Roma could have moved level with third-place Inter Milan, which is nine points below Napoli, but lost 2-1 at home to Atalanta and is fifth.
After playing over the festive period for the first time, Serie A will resume on Jan. 21.
Napoli had ended 2017 and the first half of the season as winter champions, but was eliminated from the Italian Cup on Tuesday following a surprise quarterfinal defeat to Atalanta.
Sarri's team dominated from the start against Verona and had several chances, with Dries Mertens and Insigne hitting the woodwork.
Mertens also had a goal ruled out for offside before Napoli finally broke the deadlock in the 65th minute, when Koulibaly headed in Mario Rui's cross.
The goal was awarded after checking with the video assistant referee but Verona coach - and former Napoli player and assistant - Fabio Pecchia was dismissed for his protests.
Napoli all but sealed the match 12 minutes from time when Callejon rushed in at the far post to volley in Insigne's cross from the left.
Verona remained two points from safety.
FOUR-STAR IMMOBIlE
Ciro Immobile netted four goals and moved top of the scoring charts as lazio won 5-2 at struggling Spal to move fourth.
Mirco Antenucci had converted a penalty for Spal to cancel out luis Alberto's opener before Immobile's first-half hat trick.
Immobile got his first in the 19th, running onto luis Alberto's flicked pass over the defense and lifting the ball over Alfred Gomis.
The Italy forward doubled his tally seven minutes later, firing home Sergej Milinkovic-Savic's through-ball, but Spal reduced the deficit almost immediately, with Antenucci grabbing his second of the match.
However, Immobile headed in Dusan Basta's cross four minutes before the break to complete his hat trick.
The Spal defense left Immobile completely unmarked six minutes after halftime and he drilled in a corner for his 20th league goal of the season, two more than Inter Milan forward Mauro Icardi.
FIRST FOR BONUCCI
AC Milan defender leonardo Bonucci scored his first goal for the club in a 1-0 win over Crotone - although the Italy international knew little about it.
Milan broke the deadlock nine minutes into the second half when Crotone goalkeeper Alex Cordaz flapped at a corner, sending it onto Bonucci's back and the ball rebounded into the back of the net.