Napoli lost 2-0 at home to Fiorentina, leaving last season's runners-up without a league win at their San Paolo Stadium since October 19 ahead of hosting Barcelona in the Champions League in a month's time.
Napoli fell to their third consecutive defeat and fourth in a row at home against Fiorentina.
Gennaro Gattuso replaced Carlo Ancelotti last month, but the former AC Milan boss has lost four of five games since then.
Federico Chiesa and Dusan Vlahovic scored in either half to give the Tuscany side back-to-back wins for the first time in nearly three months.
Chiesa opened the scoring on 26 minutes with Vlahovic curling in a second with quarter of an hour to go.
The southerners are in 13th position, closer to the relegation zone than the Champions League places. Fiorentina moved up to 12th.
In Reggio Emilia, Sassuolo eased their relegation fears with a come-from-behind 2-1 win over Europa League hopefuls Torino.
The hosts fell behind after Manuel Locatelli turned into his own net on 20 minutes.
But Ivory Coast international Jeremie Boga scored a stunning long-range goal after an hour and then set up Domenico Berardi for the winner on 73 minutes.
Torino, in eighth, can be overtaken by Hellas Verona and AC Milan, who play on Sunday.
Sassuolo are eight points above the drop zone.