Defending 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.
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 said. "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 while Cavani has remained stuck on 18 Serie A goals since the end of January, his recent 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.
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.
Alberto Gilardino volleyed the only goal for Bologna.
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.
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 scored from close range following a corner. The third came from a header while Maxi Lopez replied for Samp with a stoppage-time penalty.
Palermo, where coach Gian Piero Gasperini was fired and re-hired as coach in less than one month, went ahead against Siena with a close-range goal by Brazilian Anselmo just before halftime.
Switzerland midfielder Innocent Emeghara levelled early in the second half and an Alessandro Rosina penalty heaped the misery on the Sicilians who are level with Pescara at the bottom on 21 points.
Siena stayed in the drop zone but climbed to 18th and are only two points behind Genoa.
The drama continued at Parma where Mario Santana put visitors Torino ahead just before the hour only for them to be undone in a stunning finale.
Former Juve forward Amauri equalised with a brilliant volley in the 77th minute and Nicola Sansone put Parma ahead three minutes later.
Another three minutes after that, Amauri scored a solo goal then swept home a Sansone cross in stoppage time.