Mattia Caldara scored twice on Saturday to deny Napoli the chance to move second in Serie A while strengthening Atalanta's own European ambitions.
In netting both goals, Caldara became the highest-scoring defender in Italy's top flight this season, the second coming just three minutes after the visitors' highly-rated midfielder Franck Kessie was sent-off for two quickfire yellow cards.
The smash-and-grab win means Atalanta are now just three points behind Napoli, who remain two adrift of second-placed Roma.
Napoli will count themselves a touch unfortunate after twice hitting the woodwork and dominating most of the encounter at the Stadio San Paolo.
The onslaught started early, Lorenzo Insigne clipping the bar with a curling shot after just six minutes.
Despite seeing little of the ball, it was Atalanta who scored first just before the half-hour mark, Caldara nodding in at the far post after the home defence had failed to clear a corner from the right wing.
Dries Mertens almost conjured up an instant reply but his shot from inside the area flashed inches wide of the far post.
Atalanta rode their luck again on the stroke of half-time when goalkeeper Etrit Berisha tipped Mertens' curling free-kick on to the angle of post and bar.
A quiet start to the second half burst into life when Kessie was booked twice in the space of three minutes. Having been cautioned for dragging his boot down the Achilles of Amadou Diawara, the Ivory Coast international gave referee Domenico Celi little option but to book him again midway through the second period for dragging down Insigne in full flow.
Rather than prove the turning point, Atalanta promptly scored from their next attack.
Leonardo Spinazzola escaped down the left and his cross was met by Caldara, who acrobatically fired past Pepe Reina on the volley.
Piotr Zielinski drove inches wide and Jose Callejon somehow missed the target with a header from five yards as Napoli pressed for a late goal, but Atalanta held on to record their seventh away win of the season.