A defensive blunder by Napoli allowed a stoppage-time equalizer in a 1-1 draw with Torino on Sunday, hurting the southern club's title chances.
Lazio also dropped back after getting beat 4-0 by Catania, while Fiorentina was the day's big winner after beating Cagliari 4-1 to jump ahead of Lazio into fourth place.
After sitting out Napoli's last two matches with a minor injury, Edinson Cavani celebrated his return by scoring six minutes in at the San Paolo stadium from the edge of the box — his seventh goal in nine appearances this season.
But shortly after Napoli coach Walter Mazzarri was sent off for protests, Torino's Gianluca Sansone equalized with his first Serie A goal after intercepting defender Salvatore Aronica's unwise pass back to his goalkeeper.
In Sicily, Alejandro Gomez scored twice for Catania and Francesco Lodi added a penalty — all in the opening half hour — then Pablo Barrientos sealed the rout with another goal in the 69th.
In Tuscany, Gonzalo Rodriguez gave Fiorentina the lead in the 14th and Federico Casarini equalized in the 42nd after the goal-line referee intervened to overturn an offside decision. Stevan Jovetic restored Fiorentina's lead in the 50th, a rejuvenated Luca Toni found the target in the 54th, and Juan Cuadrado added another in the 85th.
Juventus, which was beat 3-1 by Inter Milan in "Italy's derby" Saturday, leads with 28 points. Inter is next with 27, Napoli has 23, Fiorentina 21, and Lazio 19.
Also Saturday, struggling AC Milan routed Chievo Verona 5-1 to move into the top half of the table.
In the Sunday night match, sixth-place Roma ended a two-match losing streak with a convincing 4-1 win over Palermo. Captain Francesco Totti put Roma ahead in the 11th and Pablo Osvaldo doubled the lead in the 31st. Erik Lamela added another for the hosts in the 69th and recent Italy call-up Mattia Destro scored his first goal for Roma in the 79th, then received his second yellow card for pulling off his shirt and will miss next weekend's derby with Lazio.
Josip Ilicic pulled one back for Palermo in the 84th.
Earlier in the lunchtime fixture, struggling Pescara beat in-form Parma 2-0 to save the job of its manager Giovanni Stroppa.
Elvis Abbruscato scored in the 49th with an angled shot from within the area, then Slovakia midfielder Vladimir Weiss sealed the win with a shot that bounced in off the post in stoppage time.
Pescara had made clear before the match that Stroppa needed to win to remain in his post. Former Catania coach Pasquale Marino had already been lined up as a replacement.
The victory moved promoted Pescara out of the relegation zone, three points clear of Palermo, which was third to last.
"It wasn't an easy buildup to the match," Stroppa said. "I read in some places that it would mark my funeral."
Parma, which had won three straight, remained sixth, tied with Catania and Atalanta, 13 points back.
Atalanta won 2-1 at Sampdoria with goals from Giacomo Bonaventura and Giuseppe De Luca. It was Samp's sixth consecutive loss, raising calls for the ouster of coach Ciro Ferrara.
Elsewhere, Antonio Di Natale scored a 73rd-minute equalizer as Udinese drew 1-1 at Bologna, which had gone ahead with a goal from Alessandro Diamanti in the 46th.
Also, last-place Siena — which has a six-point penalty for match-fixing — beat Genoa 1-0 with a 55th-minute goal from Massimo Paci.