Napoli sprint clear in Serie A
Goals from Allan, Jose Callejon and Dries Mertens helped Napoli to their 10th win in 11 matches. Diego Falcinelli had levelled for Sassuolo and both sides hit the woodwork twice.
Juventus and Lazio, who earlier won 5-1 at Benevento, are tied for second. Inter Milan are two points further back and visit Hellas Verona today. Juventus beat AC Milan 2-0, Saturday.
Napoli struggled in the opening stages on, but took control of the match, and even had the luxury of substituting three of its key players ahead of Wednesday's Champions League match at home to Manchester City.
"It's too early to talk about the title. At the moment the only thing to think about is Wednesday's match against City," Napoli coach Maurizio Sarri said. "We know it will be tough, even if we believe we can do it and have a great game."
Sarri had only one win over Sassuolo as Napoli coach, having drawn both matches last season and lost on his debut in August 2015.
Ciro Immobile turned from goalscorer to provider as he weighed in with three assists as well as a goal in Lazio's convincing victory.
Immobile set up Bastos and Adam Marusic in the first half, either side of his 14th league goal of the season moving him three clear of Inter's Mauro Icardi and Juventus forward Paulo Dybala in the scoring charts.
Achraf Lazaar reduced the deficit shortly after the break, but Simone Inzaghi brought on Luis Nani in the 70th and the former Manchester United midfielder had an immediate impact, setting up Marco Parolo before scoring his first Lazio goal after another assist from Immobile.
Promoted side Benevento have lost all 11 of its Serie A matches this season.