Prior to kick-off, Napoli had been almost impenetrable this campaign, conceding just five times in their opening 10 Serie A matches, which gave them the best defensive record in the division.
Atalanta, though, are the Italian top flight’s most prolific goalscorers, and it was the visitors’ forward line that had the upper hand during the first half, particularly Ademola Lookman.
While Romelu Lukaku had the first shot on target of the game as his tame header was easily held by Marco Carnesecchi, it was Nigeria international Lookman who broke the deadlock at the other end, crashing a close-range volley into the bottom corner following Charles De Ketelaere’s flick-on.
In response, Scott McTominay was unlucky not to equalise within seconds when his fierce effort from outside the area struck the woodwork, but that proved to be the closest Napoli came during a disappointing opening 45 minutes.
Instead, La Dea doubled their advantage, with Ballon d’Or nominee Lookman again the hero. On this occasion, however, Alex Meret really should have done better than to palm the 27-year-old’s curling attempt into the bottom corner.
Shortly before the half time whistle, Mario Pašalić almost made it three, but couldn’t quite get on the end of De Ketelaere’s inviting cross.
Napoli fans may have expected the Partenopei to come out all guns blazing after the interval, but that couldn’t be any further from the truth. Antonio Conte’s side barely laid a finger on their opponents.
In fact, Atalanta looked far more likely to extend their lead, which Lookman really should have done when he hit the side netting following a swift counterattack.
In the end, it was a serene afternoon for Gian Paolo Giasperini and Co., and they even added extra gloss to the scoreline when substitute Mateo Retegui – surprisingly left out of the starting XI – volleyed in his league-high 11th goal of the term in injury time.
Atalanta are now well in the title race after a performance like this away at one of Serie A's top outfits. Napoli, meanwhile, lose for the first time in 10 matches, although it will be the lacklustre way in which they approached the second half that will worry Conte the most.
Things don’t get much easier for the Azzurri, who travel to reigning champions Inter Milan next week in the final fixture before the international break.
Flashscore Man of the Match: Ademola Lookman (SSC Napoli)