Gli Azzurri immediately went on the front foot but almost found themselves behind inside six minutes, as Kenan Yıldız collected Khephren Thuram’s pass and sat down Leonardo Spinazzola before being denied by a superb save from Alex Meret.
The hosts kept coming and looked dangerous in the wide areas, although the Bianconeri dealt with any aerial tests well and debutant Randal Kolo Muani showed that he could cause problems with good hold-up play before Teun Koopmeiners blazed his strike harmlessly over the crossbar.
Matteo Politano came much closer with an eye-catching volley from the edge of the box, and Nico Gonzalez drove forward but fizzed his shot past the post at the other end.
Juventus then avoided a scare as Manuel Locatelli reached Michele Di Gregorio’s underhit pass ahead of Scott McTominay. Stanislav Lobotka then sent an ambitious strike marginally over, before two moments to forget for Andre-Frank Zambo Anguissa proved pivotal.
The midfielder headed over from a big opportunity, then attempted an interception, but instead touched the ball towards Kolo Muani, who clinically finished.
Politano tried to conjure a response before the break, coming agonisingly close from a free-kick he had won.
Napoli came out for the restart defiantly but Romelu Lukaku’s header was denied by an outstanding Di Gregorio save.
There was nothing the goalkeeper could do to stop Anguissa in the 57th minute, though, as he met Politano’s cross ahead of Weston McKennie to pick out the bottom corner with a far more clinical header.
Politano and Lukaku then had an effort deflected behind by Andrea Cambiaso and Federico Gatti respectively, as Gli Azzurri relentlessly looked to take the lead.
Scott McTominay earned an opening by luring Manuel Locatelli into conceding a penalty that Lukaku coolly converted by sending Di Gregorio the wrong way.
Having established their lead, Napoli were solid to see out their seventh consecutive victory and go six points ahead atop the Serie A table – although Inter Milan do have two games in hand.
They also inflicted the first defeat from Juventus’ 22 league matches this term, compounding the misery of a side with just one win from their last seven across all competitions.