Bonucci: Scudetto not won yet
Jose Callejon and Dries Mertens scored either side of the break to seal victory for Rafael Benitez's men and leave Juve sitting 11 points clear of second-placed Roma, who have a game in hand.
And Bonucci believes the result will have come as a stark reminder that the Turin outfit do not yet have their hands on the trophy.
"What this defeat really showed me is firstly that the Scudetto is still not won, and secondly that it will keep our feet on the ground," he wrote on his official website.
"You can always learn more. Napoli showed that they had more hunger than we did yesterday.
"The Juventus that I know has always shown more hunger than their opponents."
Antonio Conte's side are closing in on a third consecutive top-flight crown and have seven league games remaining, including a trip to Roma in May.