Napoli ensured Juventus' miserable start to the Serie A season continued as they held on for a 2-1 victory at San Paolo Stadium.
Massimiliano Allegri's men, who now have just five points from six matches, could find themselves 13 adrift of Inter Milan should the current leaders beat Fiorentina on Sunday night. Napoli, who followed a 5-0 win against Lazio with a disappointing goalless draw with Carpi in midweek, deserved their victory, with goals from Lorenzo Insigne and Gonzalo Higuain securing the points.
Mario Lemina scored his first goal for the Bianconeri to offer hope but they rarely threatened an equalizer. Marek Hamsik had the first shot of the game but his ambitious effort sailed over the crossbar.
At the other end, Juventus forward Simone Zaza was flagged offside as he chipped the ball over goalkeeper Pepe Reina and into the net. A first-time shot from Higuain was too high, while Reina was called into action for the first time after 14 minutes as he beat away a powerful drive from Zaza after good work from Paulo Dybala.
Insigne should have done better after cutting in from the right and letting fly with an effort that was well wide, but that was just a sighter as he opened the scoring with his third goal in six Serie A matches in the 26th minute. The Italian striker played a neat one-two with Higuain and stroked the ball past Gianluigi Buffon and into the bottom corner.
Insigne's evening took a turn for the worse in the 39th minute when he hobbled off with what looked to be a knee knock and was replaced by Dries Mertens. Jose Callejon should have made it 2-0 after Buffon parried a Faouzi Ghoulam cross into his path but the Spaniard screwed his shot wide.
And Mertens selfishly curled a shot past the post with teammates well-placed in the box as Napoli finished the half strongly. Juventus, who were looking to bounce back from a midweek draw with Frosinone, started the second half on top as Paul Pogba drilled a free-kick from a dangerous position into the defensive wall.
Higuain stung the palms of Buffon with a fierce drive on the hour as Napoli hit back, and shortly afterwards the Argentinian did make it 2-0. Sloppy play from Juventus allowed the striker to break clear and although Buffon got a strong arm on Higuain's low shot, he could not keep it out.
The Bianconeri pulled a goal back straight from kickoff as Dybala's cross found its way to Lemina at the back post and he squeezed the ball past Reina. Alvaro Morata entered the action in the 71st minute and he was inches away from an equalizer two minutes later as his low drive looked to be heading for the bottom corner.
Hamsik was withdrawn for the defensive-minded David Lopez as Napoli looked to hold on to their lead and they did so comfortably to increase Allegri's woes.