First half was rather balanced and Napoli made their best efforts to score and secure points, but just found a lucky net by Belgian Mertens. Atalanta were better in second half and well-deserved their win.
Atalanta then came back from 1-0 down to beat Napoli 2-1 at the San Paolo, courtesy of goals from Duvàn Zapata and Mario Pasalic.
That prompted Dea supporters in their droves to wait outside Orio airport in Bergamo and put on a party, complete with flares.
The result leaves the Orobici level on points with fourth-placed Milan as six teams battle for two Champions League spots in Serie A.