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 snatch the win in the final minute.
The result capped 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. It could find itself just five points ahead of Inter Milan if the Nerazzurri beat Fiorentina later.
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.
However, it was Samp which went closer in the first half. Napoli goalkeeper Morgan De Sanctis was at full stretch to palm Sansone's effort around his left post.
From the resulting corner, Samp went even closer and Valon Behrami had to head Andrea Costa's effort off the line. De Sanctis, who had mistimed his intervention, redeemed himself by saving the follow up.
Sansone went close again just before halftime with an angled drive which De Sanctis managed to parry.
Behrami again saved Napoli just after the break with a well-timed tackle, just as Mauro Icardi was about to shoot.
Mazzarri changed things around with a double substitution on the hour mark, bringing on Goran Pandev and Juan Camilo Zuniga, and Napoli began to lay seige to the Samp goal.
Hamsik went closest when his effort crashed off the right hand post and ricocheted back into the grateful arms of Sampdoria goalkeeper Sergio Romero.
Paolo Cannavaro could also have broken the deadlock with a rising effort which brushed the top of the crossbar.
Cavani went agonizingly close at the end when he toe poked an effort just wide from close range.
At the other end of the table, Genoa continued its revival under Davide Ballardini with a 1-0 win over Udinese.
It took the lead in the 33rd minute when Udinese goalkeeper Daniele Padelli flapped woefully at a corner and Juraj Kucka headed in.
Under Luigi Del Neri, Genoa won only two of 13 games, losing nine. It hasn't lost since Del Neri was replaced by Ballardini, drawing against Juventus and Parma and beating Lazio.
Genoa is now four points above 18th-placed Pescara which lost 2-0 at home to fellow struggler Cagliari.
Cagliari appealed in vain for an early penalty after Manuele Blasi appeared to foul Albin Ekdal in the area.
Pescara almost took the lead shortly before halftime but Cagliari goalkeeper Michael Agazzi palmed Vladimir Weiss' effort onto the post.
Cagliari went in front eight minutes after the interval when Marco Sau rose unmarked to head home Andrea Cossu's cross.
Sau doubled his tally when Federico Casarini backheeled Radja Nainggolan's cross and he spun and fired past Pescara goalkeeper Mattia Perin.
Weiss was shown a red card in stoppage time for a bad tackle on Victor Ibarbo.
Bologna remains five points above the drop zone after it lost 1-0 at Catania.
Sergio Almiron headed in Francesco Lodi's corner in the 42nd minute, moments after Gonzalo Bergessio's diving header had crashed off the base of the upright.
Bologna had won its past four matches against Catania, without conceding a goal.
Elsewhere, Torino beat Atalanta 2-1.
Torino dominated and took a deserved lead three minutes from halftime when Alessio Cerci beat the offside trap, racing down the right flank before cutting inside and firing a low, diagonal shot into the far corner.
Atalanta levelled after Torino goalkeeper Jean-Francois Gillet brought down Marko Livaja. German Denis' penalty squirmed under the body of Gillet, who had guessed the right way.
Valter Birsa sidefooted home Matteo Darmian's cross for the winner three minutes from time.