Matias Vecino's thumping half-volley from outside the box was enough for all three points at the Stadio Diego Armando Maradona on Friday.
Napoli dominated the match with most of the ball, but the visitors were solid in defence and kept the home side to just two shots on target all game.
The Rome side provisionally moved up to second place, with 48 points from 25 games, 17 behind Napoli ahead of the rest of the weekend's fixtures.
Third-placed Inter and fourth-placed AC Milan will both have the chance to trim Napoli's lead to 15 points if they beat Lecce at home and Fiorentina away respectively.
ANSA
