A coach-less but stubborn Sampdoria put the brakes on Napoli's Serie A title ambitions by holding the Neapolitans to a scoreless draw at the San Paolo on Sunday.
Napoli had hoped to close the gap on Juventus to just two points after the championship leaders were stunned 1-0 by Francesco Totti's rocket strike for Roma on Saturday.
But three days after a shock 3-0 defeat at home to Viktoria Plzen in the Europa League, Walter Mazzarri's side failed to conjure a goal for the second match in succession.
Despite Juve's slip-up at the Olympic Stadium the champions are still four points ahead of Napoli on 51 points, with Lazio a distant third (44) ahead of their trip to Siena on Monday.
AC Milan, 2-1 winners over Parma on Friday, are fourth also on 44 points but face being overtaken by city rivals Inter, who travel to Fiorentina for Sunday's late match.
Sampdoria had beaten Napoli only once in their last five outings, but despite missing head coach Delio Rossi, handed a two-match ban for making a rude gesture last week, the visitors went in feeling buoyed at the break.
Early on striker Gianluca Sansone worked his way through the defence to see his prodded shot smothered by Napoli keeper Morgan De Sanctis from close in.
Napoli, wearing black armbands in honour of former player Carmelo Imbriani, who died this week at the age of 37, came closest when Lorenzo Insigne unleashed a drive that forced Sergio Romero to parry.
Striker Edinson Cavani also tested Romero but should have done better with the rebound from Marek Hamsik's effort when it fell into his path.
At the other end Lorenzo De Silvestri forced De Sanctis down low to smother as the visitors dominated on the half hour.
Sansone was unlucky to see his low strike tipped around the post by an outstretched De Sanctis, who then had defender Valon Behrami to thank for clearing after he misjudged the resulting corner.
Sansone threatened once more before half-time when he tested De Sanctis with an angled shot after forcing his way past Napoli defender Gokhan Inler.
Napoli struggled in the early exchanges after the restart and had Behrami to thank for a timely clearance from Emanuele Icardi's effort only five minutes in.
It prompted Mazzarri to replace defender Miguel Britos and midfielder Pablo Armero with Goran Pandev and Juan Zuniga respectively on the hour mark.
Sansone lasted only 20 minutes of the second half and was replaced by Brazilian Eder.
Pandev's arrival, meanwhile, proved almost decisive when his short pass to Hamsik allowed the Slovakian to unleash a dangerous low shot but it came off the post and Romero scrambled to smother.
Romero had to look smart again in 78th minute when he came out to punch away a threatening cross before collecting Paolo Cannavaro's first-time strike.
Napoli were starting to find openings, but when Hamsik put Cannavaro through with the simplest of passes the defender sent his first-time effort over the bar.
Napoli were to rue those missed chances as Sampdoria increased the pressure in the dying minutes with a series of counter-attacks which had the hosts on the ropes before they were forced to settle for a morale-sapping draw.
Meanwhile, Catania continued their fairytale campaign with a 1-0 win at home over Bologna which moved them up to seventh and within sight of the European places.
Torino moved up two places thanks to Valter Birsa's 87th-minute winner in a 2-1 victory over Atalanta, while Juraj Kucka's 33rd-minute goal was enough to see Genoa move further away from the drop zone with a 1-0 win over Udinese.
A Marco Sau double for Cagliari assured a 2-0 win away to new boys Pescara and moved the Sardinians up to 14th.