Napoli missed the chance to cut Juventus' lead to two points as it was held to a 0-0 draw at home by Sampdoria in Serie A on Sunday.
Sampdoria had the better of the chances, notably through Gianluca Sansone, as Napoli was pegged back into its own half for most of the opening period.
Marek Hamsik hit the post in the 74th minute as Napoli improved after the break. Edinson Cavani missed a chance to seal the win in the final minute. The result caps a miserable week for Walter Mazzarri's team following its 3-0 loss at home to Viktoria Plzen in the Europa League on Thursday.
Napoli remains second, four points behind Juventus.
Sampdoria had lost on its past four visits to Napoli, without scoring a goal, and has not won at the San Paolo since the 1997-98 season.
In Sunday's late game, Fiorentina rejoined the hunt for a Champions League place with a resounding 4-1 win over Inter Milan at the Stadio Artemio Franchi.
Udinese, meanwhile, lost ground on its European rivals after two gilt-edged chances to force a draw went begging at the end of a 1-0 defeat at Genoa.
Davide Ballardini earned his second win since replacing Luigi Del Neri as Genoa boss when Juraj Kucka nodded the hosts ahead in the first half.
Two goals from Marco Sau lifted Cagliari away from the relegation zone and left Pescara in real danger as the Sardinians won 2-0 at the Stadio Adriatico.
After a tight first half in which both sides took a cautious approach, Cagliari emerged with more conviction and Sau struck twice early in the second half to earn the points.
Pescara ended the game with 10 men with Vladimir Weiss sent off in stoppage time as the home fans made their feelings heard.
Elsewhere, an 87th-minute goal by Valter Birsa guided Torino to a 2-1 victory as it won for the first time in four Serie A games.
Information from Press Association and The Associated Press was used in this report.