The visitors came within inches of taking the lead just before the half-hour mark when Edinson Cavani smashed a free kick against the Juventus crossbar.
The hosts responded with a chance of their own right on the stroke of half-time, Claudio Marchisio forcing a save from the opposition keeper with a fine 20-yard strike.
The best chance of the opening hour fell to Sebastian Giovinco in the 57th minute when he had plenty of time to pick out a corner from 10 yards out but could only skew his shot well wide of the post.
Just two minutes later the hosts doubled their lead when Paul Pogba unleashed a superb first-time volley from 25 yards out to all but kill the game off.
Napoli looked for an unlikely comeback, but Juventus held out to extend their unbeaten record in the league to 47 games.