Marek Hamsik found Jose Maria Callejon on the right and he crossed for Duvan Zapata to tap in for his first league goal.
Callejon doubled the visitors’ advantage, before Henrique scored his first Napoli goal with a strike from the tightest of angles.
Zapata all but sealed the match on the stroke of halftime, although Catania attempted a comeback in the second period as defenders Fabian Monzon and Norbert Gyomber also scored their debut league goals.
Fiorentina forward Alessandro Matri, who is on loan from AC Milan, missed a couple of early chances against his old team and it was the under-fire visitors who took a surprise lead in the 23rd minute.
Balotelli had been dropped for the weekend draw against Lazio, but he returned to the starting lineup and fired in a free-kick which was parried by Neto, but straight to Philippe Mexes, who headed in.
Balotelli doubled Milan’s advantage with another free-kick into the top-right corner in the 64th minute.
Fifth-placed Inter could close the gap on ACF Fiorentina to just one point with victory at home to Udinese yesterday.
Parma are currently level on points with Inter, with Atalanta four points below the final Europa League spot following a club record fifth consecutive win.