First-half goals from Duvan Zapata, Jose Callejon and Henrique made the final outcome look like a foregone conclusion but bottom side Catania hit back through Fabian Monzon and Norbert Gyomber.
The Azzurri sensibly decided to shut the game down and successfully put three more points on the board in their bid to catch second-placed Roma, who are now only six points better off in Serie A.
Catania remain bottom of the pile and look set to return to the second tier after eight years away.
The Sicilian basement boys were never likely to worry Champions League-chasing Napoli but that option was ruthlessly taken from them by force.
It appeared Mariano Andujar might have a good night in the home goal when he denied Lorenzo Insigne from close range after two minutes.
He soon punched Blerim Dzemaili's fiercely-struck free-kick clear before watching calmly as Insigne screwed a shot high over the bar.
But in the 16th minute, Napoli plundered their first goal and never really looked back.
After Marek Hamsik freed Callejon in the final third, the Spaniard drove a low ball into the D and Zapata pinged it home with his left boot.
Catania would hit the crossbar through Pablo Barrientos before conceding again in the 25th minute.
This time Andujar's path to gathering the ball was blocked by defender Nicola Legrottaglie and Callejon gratefully took Insigne's pass and found the empty net.
Callejon missed a chance to make it 3-0 shortly after the half-hour when looking for the top corner with a sighter, but it would not matter.
January signing Henrique opened his Serie A account for Napoli with an extraordinary strike that completely bamboozled Andujar.
The invigorated Partenopei fancied a fourth goal before the break and found it through Zapata, who thought he had ended the game as a contest with a right-footed daisy-cutter.
But no one told Catania they had already lost the game during the half-time interval, though, and they promptly pulled a goal back seven minutes after the restart.
Keko had just rattled Jose Reina with a snapshot and Monzon capitalised on the goalkeeper's lapse in concentration to beat him with a speculative effort off his left boot.
At this point Napoli, perhaps exhausted from their first-half exertions, hit the snooze button.
As a result, in the 75th minute Catania managed to halve the deficit against all odds as Slovakian defender Gyomber nodded home from an inswinging corner.
Coach Rafael Benitez yelled at his players to wake up and batten down the hatches and they did so, Francesco Lodi's searing drive representing Catania's last solid chance to get back into the tie.