Late goals from Juventus striker Gonzalo Higuain and substitute Paulo Dybala were not enough to secure the Old Lady victory as the Italian champions stumbled to a 3-2 defeat away to Sampdoria on Sunday.
The hosts dominated the game as goals from Duvan Zapata, Lucas Torreira and Gianmarco Ferrari ensured that the added-time Juventus response was only a consolation.
Napoli remain four points clear at the top of Serie A as Sampdoria maintained their unbeaten spell at the Stadio Luigi Ferraris this season.
Argentine Higuain had a chance inside the opening two minutes to put the visitors in front, but his deflected effort trickled past Emiliano Viviano's post.
The hosts were barely in the game throughout the first half and failed to muster a decent chance as Juventus dominated. Juan Cuadrado was influential in the first period, as he found Mario Mandzukic, whose touch let him down.
Former Chelsea man Cuadrado then had a golden opportunity just after the half-hour mark but he opted to shoot wide of Viviano's goal instead of pulling the ball back to the expectant Mandzukic.
Sampdoria's only decent spell in the first half came and went as Gaston Ramirez fouled Stephan Lichtsteiner.
The home side were immediately on their game in the second half, though, and they took the lead on 52 minutes through Zapata, who rose above Lichtsteiner to head past Wojciech Szczesny.
Zapata could have had a second when he was played through four minutes later, but ex-Arsenal stopper Szczesny won that particular battle.
Sampdoria were not disheartened however, and pressed for another. Marco Giampaolo's side found it after 71 minutes when midfielder Torreira struck to double his side's lead.
Douglas Costa replaced Cuadrado soon after as Juve coach Massimiliano Allegri turned on the offensive, but Gianmarco Ferrari sealed the win as he snuck ahead of a complacent Sami Khedira to squeeze home.
Sampdoria could also have been blamed for complacency in the final stages too, as Higuain converted from the penalty spot just after 90 minutes.
Dybala then danced through the hosts' defenders to slot home Juve's second, but Allegri's team were too late in turning up to the contest.
