Mario Balotelli also scored twice to give third-placed AC Milan a 2-0 win over joint bottom club Palermo where Giuseppe Sannino started his second stint of the season as coach of the volatile Sicilian club.
Pescara stayed level at the bottom with Palermo after losing 2-0 at home to Chievo while Siena missed a chance to move out of the relegation zone when they were held 0-0 at home by Cagliari.
Fourth-placed Fiorentina twice surrendered the lead at home to Genoa before a Mattia Cassani own goal gave them a 3-2 win.
Cavani has scored 20 Serie A goals this season while Balotelli has scored seven in six appearances for Milan since his move from Manchester City. Napoli, who have 56 points, are nine behind leaders Juventus and two ahead of Milan.
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