Leaders Juventus took full advantage when a stoppage-time goal by Emanuele Giaccherini gave them a 1-0 home win over Catania, taking them nine points clear with 10 games to play.
Inter Milan's Champions League hopes took a knock with a 1-0 home defeat by mid-table Bologna, earning them a chorus of jeers at the San Siro, and Fiorentina went fourth by winning 2-0 at Lazio.
Colombian Victor Ibarbo scored a hat-trick to give Cagliari a 3-1 win over Sampdoria, although as in their previous games, there were no fans there to watch it due to safety problems at their improvised Is Arenas home.
At the bottom, Siena came from behind to win 2-1 at Palermo in a meeting of two teams mired in the relegation zone and Pescara's new coach Cristian Bucchi made a losing start as the bottom side lost 2-1 at Atalanta.
Mid-table Parma scored four goals, including a brilliant Amauri ha-trick, in the last quarter of an hour to beat Torino 4-1 at home.
Champions Juventus have 62 points while Napoli, on 53, are only two clear of third-placed AC Milan, who won 2-0 at Genoa on Friday. Fiorentina are next with 48 points after leap-frogging both Inter and Lazio who both have 47.
Napoli coach Walter Mazzarri, who needs a top-two finish to qualify directly for the Champions League, was philosophical in defeat.
"They had two shots, two goals," he told reporters. "It's football, there are times when things go well and times when things go badly."
Mazzarri's team had drawn their previous four league games and Cavani has remained stuck on 18 Serie A goals since the end of January, his goal drought including two Europa League matches.
It went from bad to worse as Boukary Drame fired Chievo ahead with a long-range shot after 12 minutes and Cyril Thereau broke clear to add another two minutes before the break.
Uruguay forward Cavani had a chance to bring Napoli back into the game when he won a penalty but his poor kick was saved by Christian Puggioni.
Juventus struggled to break down a stubborn Catania and had to wait until the 91st minute when Giaccherini turned in a rebound, one minute after being booked for diving in the penalty area.
It was Catania's second successive stoppage-time defeat following a 3-2 loss to Inter Milan.
Alberto Gilardino volleyed the only goal for Bologna as they beat Inter at a restless San Siro and goals in each half from Stevan Jovetic and Adem Ljajic, the latter a curling free-kick, gave Fiorentina a crucial win at Lazio.
Cagliari, whose president Massimo Cellino was put under house arrest on charges of embezzlement in the extension of the Is Arenas stadium, continued to climb away from the relegation zone despite another empty house.
Ibarbo's first effort was a tap-in after 17 minutes and his second, early in the second half, was also
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