The Senegalese defender's victor sees Napoli close up to within one point of Juve, with four games left in the season.
The match was a nail-biter, with Napoli nearly notching an early goal when winger Lorenzo Insigne fired a shot that went wide.
Juventus lost Giorgio Chiellini to injury and his absence could be crucial over the next four games.
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Juventus had to reshuffle their defence after Giorgio Chiellini limped off injured in the 11th minute although they almost went ahead with a Miralem Pjanic free kick which was deflected on to the post.
Napoli had the ball in the back of the net as half-time approached, Insigne prodding home only for referee Gianluca Rocchi to rule that the Italy striker had been offside.
Juventus coach Massimiliano Allegri has stressed the Old Lady need "something extraordinary" to win the Scudetto in the 2017/18 season.
"It's a head-to-head and anything can happen in those situations". We are still in the lead of Serie A, we have two games at home and two away, but the decisive one will be in Milan.
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"There are still some games to go, but we want to win them all and then we'll see".
"Napoli deserve some credit for their victory, but there were barely any chances".
The title race will go down to the wire because there are no easy matches for either side. We should have done better in possession and not rushed around so much when they had it.
Despite going toe-to-toe with Juventus for the majority of the Serie A season, Napoli's title challenge seemed to be disappearing without a whimper. We will carry on giving 110%, but Juventus are ahead of us and their win percentage is impressive.
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