Second-half goals from Jose Callejon and Lorenzo Insigne earned Napoli a 2-0 win in Nice and ensured their qualification for the Champions League group stages.
The Serie A side won 4-0 on aggregate but it could have been more with Dries Mertens also striking the post and missing several opportunities in a game they largely dominated.
After a frustrating first half, Callejon opened the scoring from close range in the 48th minute from a Marek Hamsik cross while Mario Balotelli was on the sideline receiving treatment.
Insigne's well-placed effort from the edge of the box in the 89th minute wrapped up proceedings.
Nice, who started with Balotelli, Wesley Sneijder and reported Barcelona target Jean Seri in their side, did rally after going behind but were unable to break down a superior side.
The Ligue 1 outfit will now play in the Europa League for a second consecutive campaign.