A 5-1 thrashing of Frosinone helped Napoli reach the Serie A summit at the season's halfway stage after Inter suffered a last-gasp defeat to Sassuolo.
Being crowned 'winter champions' may hold significance for the San Paolo side, who were also top of the pile at the same stage when they last won the Scudetto in 1990.
Andrea Consigli's heroic performance in goal for Sassuolo and a last-gasp Domenico Berardi penalty at San Siro put Roberto Mancini's Inter under threat in top spot, and Napoli capitalised in ruthless fashion.
Maurizio Sarri's men dominated from the start at the Stadio Comunale Matusa and deservedly went a goal up after 20 minutes, as Raul Albiol found the net from close range following Jorginho's corner.
Gonzalo Higuain scored from the penalty spot on the half-hour and took his tally for the season to 18 just a minute after Marek Hamsik had put Napoli three goals to the good in the second half.
Manolo Gabbiadini replaced Higuain and got in on the act himself with the visitors' fifth and Paolo Sammarco netted a consolation goal late on.
Genoa recorded an important 2-0 away win over Atalanta following late goals from Blerim Dzemaili and Leonardo Pavelotti, while a single Franco Vazquez strike saw Palermo defeat Verona at the Bentegodi.
Bologna were beaten 1-0 at home by Chievo, with Simone Pepe scoring the winner in the 79th minute after Mattia Destro had previously missed a penalty for the hosts.
Finally, veteran striker Massimo Maccarone scored his eighth goal of the season to help Empoli ease past Torino.