Napoli made it 10 league wins in a row as they moved four points clear at the top of Serie A by thumping Cagliari.
Juventus had their game against Atalanta postponed on Sunday because of snow and Napoli took full advantage on Monday.
Jose Callejon opened the scoring with a curler, before Dries Mertens stabbed in his 15th of the season at the near post and Marek Hamsik bent in a fine goal.
Lorenzo Insigne added a penalty and Mario Rui then scored a stunning last-minute free-kick, according to a BBC report.
Napoli have not won the league since 1990, when Diego Maradona was playing for them.
They have only lost once all season - to Juventus in December - and were in frightening form in Cagliari.
Napoli went out of the Europa League last Thursday, so can focus on Serie A, while Juve, who have won the league for each of the past six seasons, must contend with a trip to Wembley to face Tottenham in the Champions League.
With games against top-five sides Roma and Inter up next, Maurizio Sarri's side could face a vital few weeks.
