A second-half goal from Marek Hamsik took Napoli up to second in Serie A, just two points behind league leaders Juventus, thanks to a 1-0 win at Cagliari.
Walter Mazzarri's side struggled to impress and, after hitting the post early on, the Partenopei spent most of the time defending.
Cagliari hit the woodwork twice and looked more likely to score until Hamsik pounced on a loose ball to earn the visitors all three points and take them above Inter Milan and Fiorentina.
Lorenzo Insigne rattled the post at the end of a rare Napoli attack in the 21st minute, but Cagliari were largely the livelier of the two teams in the first half.
Alessandro Gamberini almost gave Napoli the lead when he diverted a corner against his own post, before Danilo Avelar tried a speculative lob from 35 yards which landed on the roof of the net after De Sanctis had left his goal vacant.
A goalmouth scramble saw Michael Agazzi called into action twice on the hour mark before Hamsik put Napoli ahead with a rare attack in the 72nd minute.
Juan Zuniga put pressure on Albin Ekdal, who nudged the ball inadvertently to Hamsik to curl into the far corner from eight yards.
It was harsh on Cagliari, who tried to find an equaliser, but the Rossoblu were unable to find one.
Inter Milan failed to take advantage of Juventus' defeat to AC Milan on Sunday as they fell to a 1-0 defeat at Parma.
Nicola Sansone scored the only goal of the game 15 minutes from time to give Parma a deserved win at the Stadio Ennio Tardini.
Inter were once again off colour, losing for the second time in three games since beating Juve 3-1 in Turin.
Parma certainly had no fear and continued to attack their opponents, whose only shot in the first half came from Esteban Cambiasso, but the ball was blocked on the line.
Jonathan Biabiany was particularly inspired against his former club and his shot in the 44th minute flew just wide of the far post with Handanovic standing idly by, unable to intervene even had the shot been on target.
Parma gained a deserved lead in the 75th minute when Sansone picked up possession inside his own half and set off on a 30-yard run which culminated in a low shot into the bottom left-hand corner of Handanovic's goal.
Parma easily held on to the win which lifted them to seventh in the table and above AC Milan, maintaining an unbeaten home record that stretches back to March.