After drawing with Fiorentina and Sampdoria in Serie A either side of a 0-0 stalemate with Atletico Madrid in the Champions League, Juventus took an early lead through Carlos Tevez after three minutes.
Arturo Vidal doubled the advantage 12 minutes later and Fernando Llorente added another five minutes after the break, before Luca Rossettini grabbed a consolation for Cagliari.
Juve are top with 39 points from 16 games, four ahead of second place AS Roma, who play at AC Milan on Saturday, with Napoli third on 27.
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"Nowadays football matches can never be considered finished, even when you are winning 3-1," Juventus coach Massimiliano Allegri said. "After scoring to make it 2-0 we took a risk to chase another goal."
Zdenek Zeman's Cagliari are third from bottom with 12 points.
Duvan Zapata opened the scoring for Napoli with a wonderful goal after 19 minutes from a cross by Christian Maggio and Dries Mertens converted a penalty 11 minutes later following a foul by Massimo Gobbi on Jose Callejon.
Parma are rooted to the foot of the table with six points.
Juventus play Napoli in the Italian Super Cup final in Doha on Monday. Juventus have won the trophy six times, while Napoli's only success in the competition came in 1990 with Argentina great Diego Maradona on the pitch.
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