There could have a 100th strike too, but after completing his treble Cavani missed a penalty.
He scored after 18 minutes with a deflected effort to make the breakthrough, after 30 minutes to put Napoli firmly in charge, and after 63 minutes with a solo effort.
Looking to complete his century of goals in the 76th minute, he rapped his penalty over the Lazio bar.
Victory moved Napoli level with Juventus at the top of the table, with both sides having 13 points from five games and identical goals scored and goals conceded records.
AC Milan eased the pressure on head coach
El Shaarawy's 15th-minute opener was the Rossoneri's first goal at the San Siro this season and his classy second strike eight minutes from the end sealed a first victory in front of the home faithful.
Inter Milan was a comfortable 2-0 winner at Chievo,
Roma was held 1-1 at home by Sampdoria, which equalised after going down to 10 men.
But Sampdoria defied expectations by drawing level after 62 minutes when
Nicolas Spolli and Gonzalo Bergessio were on target for Catania in the 52nd and 65th minutes after Atalanta had edged ahead through
A wonder goal from
Palermo shrugged off the disappointment of two disallowed
But Pescara kept chipping away at Gian Piero Gasperini's tiring side, and Weiss' thunderbolt in the 86th minute condemned the Palermo boss to a second consecutive straight defeat since he replaced
Torino and Udinese drew 0-0 in the night's other match.
UAE Pro-League champion Al Ain finished its campaign with a 2-1 victory over Al Nasr.