Dries Mertens ended his goal drought to help Napoli to a slender 1-0 victory at Atalanta on Sunday as Maurizio Sarri's team extended its lead at the top of the Serie A standings.

Napoli moved four points clear of six-time defending champion Juventus, which hosts Genoa on Monday.

Lazio went third with a 5-1 win over Chievo Verona. It is 11 points behind Napoli, albeit with a match in hand, and a point above Inter Milan which hosted fifth-placed Roma later.

Midtable AC Milan was also playing later, at Cagliari.

Napoli was looking for revenge after losing the Italian quarterfinal to Atalanta at the beginning of the year but struggled to create anything against a very well-organized defense.

Lorenzo Insigne went closest in an even first half, with a curling shot which was deflected just past the top corner.

Atalanta goalkeeper Etrit Berisha parried Jose Callejon's header from point-blank range and Andrea Masiello cleared the rebound off the line early in the second half as Napoli began to look more dangerous.

The visitors broke the deadlock in the 65th minute as Mertens beat the offside trap to run onto Callejon's through-ball and smash it in for his 11th league goal this season but his first in 10 Serie A matches.

Atalanta had chances to level, while Napoli substitute Marek Hamsik blazed over the bar from a good position.

Hamsik also had a goal ruled out for offside in stoppage time.

___

IMMOBILE WORRY

Lazio could be left counting the cost of its impressive 5-1 victory over Chievo as it lost Serie A top goalscorer Ciro Immobile to injury.

Immobile, who has scored 20 goals in the league this season, pulled up in the 34th minute clutching his thigh and immediately asked to be replaced.

Sergej Milinkovic-Savic had put Lazio 2-1 up minutes earlier. Luis Alberto opened the scoring for Lazio but a defensive lapse allowed Manuel Pucciarelli to level less than a minute later.

Chievo thought it had a chance to equalize in first-half stoppages as it was awarded a penalty after Senad Lulic appeared to trip Mariusz Stepinski but the referee changed his mind on video review.

Milinkovic-Savic doubled his tally in the 68th, and Juan Bastos and Nani extended Lazio's lead late on.

___

OTHER MATCHES

Fabio Quagliarella scored a hat trick against his former club as Sampdoria beat Fiorentina 3-1.

Elsewhere, Crotone moved out of the bottom three as it won 3-0 at 10-man Hellas Verona in a relegation fight.

Crotone moved two points above Spal which drew 1-1 at Udinese.

Bottom-side Benevento lost 3-0 at Bologna while Sassuolo drew 1-1 against Torino.