Lazio's 18-year-old substitute Keita Balde scored a brilliant solo goal but it was not enough to stop them sliding to their fifth league defeat of the season.
Argentina striker Higuain put Napoli in front at a half-empty Stadio Olimpico when he collected the ball just inside the Lazio half, powered through the midfield and slipped his shot cleverly under Federico Marchetti.
Unfortunately for Napoli, Swiss midfielder Velon Behrami put through his own goal less than a minute later and they had to start all over again.
Lazio, however, offered little threat and Goran Pandev put Napoli back in front five minutes after the re-start, the Macedonia forward being given far too much time to turn after Christian Maggio knocked down a cross.
Pandev then set Higuain clear with a perfectly weighted pass and the former Real Madrid forward calmly slotted his shot into the corner of the net for his seventh goal of the season.
Spanish-born Balde, a product of Barcelona's youth academy, gave the hosts hope when he weaved past three defenders and confidently fired home with two minutes of normal time left.
But Jose Callejon wrapped up the victory for Napoli in stoppage time after Lazio lost possession in midfield.
Fiorentina's Serie A leading scorer Giuseppe Rossi converted a second-half penalty to secure the points in a topsy-turvy encounter earlier on Monday which left them equal fourth with Inter Milan on 27 points and promoted Verona sixth with 22.
The teams shared four goals in a remarkable opening quarter of an hour as Borja Valero put Fiore ahead in the fifth minute but Romulo levelled within a minute before Juan Iturbe gave the visitors the lead and Valero then equalised again.
Peru midfielder Juan Vargas gave Fiorentina a halftime lead with an angled shot and Rossi scored what turned out to be the winner with a 54th-minute penalty awarded for a handball by Bosko Jankovic, who was sent off.
It was Rossi's 12th goal in a season which has seen him make an impressive comeback after a knee injury sidelined him for the best part of two years.
Despite playing with 10 men for most of the second half, Verona managed to pull a goal back in the 72nd minute when Jorginho scored from a rebound.