Napoli surrendered the lead to lose 3-2 at home to Atalanta on Saturday, dropping from first to third as the gap between the top four sides in Serie A was squeezed to four points.
Luciano Spalletti's hosts recovered from a goal down and went in front early in the second half, only for the visiting Bergamo club to mount a comeback of their own and inflict a second league defeat of the season on the hosts.
The result saw Napoli, who had led the title race since week four, remain on 36 points, two behind new leaders AC Milan, one behind Inter Milan and two ahead of fourth-placed Atalanta.
Ruslan Malinovskyi blasted a shot into the top corner to put the visitors in front after seven minutes but Piotr Zielinski fired home an equaliser near the end of a high tempo first half.
Dries Mertens then sprang the offside trap and tucked in a composed finish for his fifth goal in four league games early in the second half, but Atalanta responded superbly.
Duvan Zapata powered a header off the post as a warning sign before Merih Demiral raced onto a through ball to smash home an equaliser in the 66th minute and Remo Freuler guided the winner into the bottom corner five minutes later.