If this was just the antipasto, Napoli should be concerned about what AC Milan will serve up for the main course.
In the first of three matchups between Milan and Napoli this month, the defending Serie A champions routed this season's runaway leaders 4-0 on Sunday ahead of two more clashes in the Champions League quarter finals.
Rafael Leao scored twice and Brahim Diaz set up one goal and scored another to hand Napoli their heaviest defeat of what otherwise has been an extraordinary season.
"We're happy with the performance but it's just one game," Milan coach Stefano Pioli said. "Tonight's (Sunday) result has nothing to do with the Champions League games, because that's a different competition. That will be a very balanced contest."
Napoli's only other losses in the Italian league this season both came by scores of 1-0, to Inter Milan in January and to Lazio a month ago.
Napoli were also beaten 2-0 by Liverpool in the final match of the Champions League group phase but that loss came after the Partenopei had already clinched a spot in the round-of-16.
Otherwise, Napoli's only other defeat in 2022-23 came against Cremonese on penalties in the Italian Cup.
Milan moved up to third place, 20 points behind Napoli and four points behind Lazio.
Milan controlled from the start at the Diego Armando Maradona stadium and Diaz set up Milan's early opener for Leao with a perfect through ball. Leao — last season's MVP — then did the rest by chipping in over Napoli goalkeeper Alex Meret.
Diaz produced some more fireworks when he faked out Mario Rui to score from close range in the 25th minute.
It marked the first time that Napoli conceded twice in the opening 25 minutes of a Serie A game since a match against Juventus in August 2019.
Leao fired in the third from a sharp angle near the hour mark after deceiving Napoli defender Amir Rrahmani.
Then Alexis Saelemaekers weaved through Napoli's defence less than 10 minutes later to complete the rout.
At the final whistle, Leao exchanged shirts with his fellow left winger at Napoli, Khvicha Kvaratskhelia.
"I'm a big fan of his," Leao said. "I like what he does on the pitch."