Inter Milan ended Napoli's winning streak in Serie A with a goalless draw in Saturday's top of the table clash.
Napoli have 25 points from nine games to hold their two-point advantage on second-placed Inter.
Champions Juventus and Lazio -- joint third on 19 points -- now have a golden opportunity to narrow the gap on Sunday when they take on Udinese and Cagliari respectively.
Napoli had been on a winning streak in 13 Serie A games going back to last season.
But they came up against a stubborn Inter, chasing a first win in Naples in 20 years, and who underlined their title credentials in front of 50,000 spectators at the San Paolo Stadium.
Both teams had their goalkeepers to thank for the stalemate with Inter's Samir Handanovic and Napoli's Pepe Reina pulling off some fine saves.
Napoli had more possession in the first half but little to show for their efforts as Handanovic kept out a quickfire double from Jose Callejon and Dries Mertens.
Reina also pulled of some dramatic saves denying Mauro Icardi and Borja Valero just before the break.
Just on half-time Callejon went into a sliding tackle and doubled up in pain but but was able to walk off the pitch.
Napoli ran out of steam in the second half showing signs of fatigue after their Champions League defeat at Manchester City on Tuesday.
Inter with no European commitments looked fresher but Napoli nevertheless had the two best chances to break the deadlock with Piotr Zielinski's long range volley on 84 minutes and Mertens six minutes later cleared by Handanovic.
Earlier Sampdoria crushed struggling Crotone with a five-goal blitz to move fifth.
The Genoa club, who have a game in hand, were three goals up by half-time with Gianmarco Ferrari heading in after three minutes against his former club.
Fabio Quagliarella converted a penalty on 11 minutes after Arlind Ajeti dragged down Duvan Zapata, with Gianluca Caprari tapping in a third before the break.
Croatian forward Ante Budimir looked to have got one back for the Calabrians before half-time but the video referee confirmed his header did not cross into the goal.
Polish pair Karol Linetty and substitute Dawid Kownacki added two more for good measure in a five-minute spree from 71 minutes as Sampdoria kept their perfect home record.
Crotone -- with 19 goals conceded in nine games -- are just one point above the relegation zone after a fifth defeat.
© 2017 AFP