The visitors may have played the better football at the San Paolo, but their failure to defend as a unit and take their chances allowed El Matador to swoop in for all three points
Edinson Cavani was not in a forgiving mood as he scored a hat trick to inspire his side to a significant victory over Zdenek Zeman's capital outfit, and despite Pablo Osvaldo's consolation, Christian Maggio secured the result in stoppage time.
The Partenopei got going inside four minutes, however, through Cavani. The Roman defense was all at sea as Goran Pandev was afforded the time and space to pick his spot and slip through the Uruguayan, who tucked the ball home.
Roma was not prepared to back down and they proceeded to rain shots at Morgan De Sanctis' goal. Firstly, another pinpoint pass was latched onto by Mattia Destro, but the young forward could only manage a toe-poke's worth of contact.
Soon after, it was Erik Lamela's turn to test the shot-stopper from distance, but the Argentine's drive from distance was tipped over the bar by the veteran. Further snapshots followed, but the hosts hung on to their advantage at halftime.
Yet Napoli doubled its tally - again only four minutes after the break. This time, a low ball was pulled across goal, and Roma's failure to deal with the situation allowed Pandev to squeeze a layoff in the box for Cavani to gently lift over Mauro Goicoechea.
The Giallorossi stayed loyal to their crisp passing game and pressurized approach but lacked the final pass on frequent occasions, and it presented Napoli the chance to hit its opponent on the counterattack, which almost proved fatal.
The visitors' backline was caught unaware by the rapid movement of Napoli's front players, and Marek Hamsik was left kicking himself when his touch to take the ball past Goicoechea was too strong, while Cavani also came close.
However, they nonetheless made it 3-0 on 70 minutes when Pandev's telepathic understanding with Cavani was demonstrated yet again - the FYROM international's corner was headed down and over the line by the hat-trick hero.
Roma did conjure up a late consolation, though, just two minutes later, as substitute Osvaldo made an instant impact, reading Miralem Pjanic's inch-perfect through ball to slot the ball past De Sanctis, but it was too little, too late.
Still, there was time for a moment of madness from Pjanic, who was given his marching orders after his lunge into the back of a Biancazzurri jersey was deemed a second bookable offence.
Michael Bradley was then guilty of ballooning a pair of headers in quick succession, while Osvaldo saw a free attempt loop over the bar, and predictably a Napoli counter would round off the rout on 90 minutes when Maggio buried his rebound.
Roma has now lost two of its past three league matches but stay sixth, while Napoli is now just seven points shy of leader Juventus.