Napoli's hopes of closing the gap on Juventus at the top of Serie A to two points were dashed on Sunday following a subdued performance in a 0-0 home draw with Sampdoria.
Fiorentina, shaping up as rivals to Napoli in the chase for a Champions League spot, got back to winning ways with a 4-1 thrashing of dismal Inter Milan.
With leaders Juve losing 1-0 at AS Roma on Saturday, second-placed Napoli were looking to put the pressure on their Turin rivals and bounce back after a 3-0 home Europa League defeat by Viktoria Plzen.
After a minute's silence to remember former Napoli player Carmelo Imbriani, who died of cancer on Friday at the age of 37, it was the visitors who came out in determined mood with Gianluca Sansone going close.
Napoli responded well, though, with Lorenzo Insigne letting fly from distance and Edinson Cavani fluffing a shot into the arms of goalkeeper Sergio Romero.
Goran Pandev came off the bench to link up nicely with Marek Hamsik whose powerful shot was only kept out by a full-stretch Romero.
Juventus, however, remain in touching distance just four points above with the two sides due to meet next month.
Napoli coach Walter Mazzarri did not speak to the press but sporting director Riccardo Bigon said this was because of illness.
"We remain convinced that we have our future in our hands," he said. "We created plenty of chances against Sampdoria, we're still optimistic about our chances in this title race.
"Mazzarri? He's not well. He's got a 38-degree temperature, he's gone home to get some rest."
Sampdoria assistant coach Fedele Limoni was delighted by his side's performance.
"We worked really hard defensively, we gave very little away to Napoli," he said. "The pitch? It's the same for everybody. It was a problem for us when it came to trying to find space, it certainly did affect us."
Goals from Adem Ljajic and Stevan Jovetic ensured a comprehensive win for Fiorentina over Inter in front of an ecstatic home crowd.
Fiorentina dominated the first half and it was only a fine display from keeper Samir Handanovic that kept the scoreline respectable.
Fiorentina took the lead in the 13th minute after Jovetic flicked a cross by Manuel Pasqual to Ljajic who got in front of defender Juan Jesus to beat Handanovic with a diving header from close range.
Jovetic then shrugged off the attentions of Andrea Ranocchia before curling in a fine shot from the left-hand side of the penalty area with the keeper rooted to the spot.
The Montenegrin got his second, set up by a neat Alberto Aquilani back heel that left him free to hit a powerful right-foot shot past Handanovic and Ljajic made it four in the 65th minute.
Antonio Cassano's late consolation aside, this was humiliating for Inter who face the remainder of the season without injured striker Diego Milito.
There were also leapfrogged by city rivals Milan who sit fourth in the standings, rejuvenated by former Nerazzurri player Mario Balotelli and with the Milanese derby looming next weekend.
"We're all really happy," Jovetic told reporters. "This was pretty much the perfect game, maybe the best of the season.
"This could be a real turning-point, we're going to enjoy the victory, but we can't get distracted, it's so easy to slip up in this championship and slide down the table."
Shell-shocked Inter coach Andrea Stramaccioni said his side were too bad to be true.
"I believe that in this championship you can still suffer a defeat like this and stay in contention: remember that Milan lost 4-2 to Roma not so long ago.
"We looked tired, maybe we paid for our good work in the Europa League on Thursday. Maybe I also made the wrong choices."
Struggling Pescara lost 2-0 to Cagliari and Torino earned three points with a 2-1 home win over Atalanta.
Genoa, easing clear of the drop zone, saw off Udinese 1-0 and Catania are seventh thanks to a 1-0 win over Bologna. Siena host Lazio on Monday.
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