Napoli, who had star striker Victor Osimhen injured, were thrashed 4-0 by AC Milan on Sunday night.
Rafael Leao grabbed a brace to give his side victory over the Serie A leaders.
It also moved Stefano Pioli’s side up to third place in the standings.
Milan have 51 points, one ahead of fourth-placed Internazionale, and are four behind second-placed Lazio. Napoli are 20 points clear at the top.
“This is only the first step. There are another nine Serie A games where we must have the same attitude, because we threw away opportunities in the past and cannot do it again. This is a fine win, but it is only one match,” Pioli told DAZN.
The match was the first of three clashes between the clubs. Later this month, they will also play against each other in the Champions League quarterfinals.
“Whatever the result was going to be this evening, it would not affect the Champions League, as that will be a different experience, atmosphere and everything. It will allow us to study this match and see where we did well or could’ve done better,” Pioli added.
The visitors went ahead after 17 minutes when Brahim Diaz sent a through ball to Leao, who took a touch and chipped it elegantly over Napoli goalkeeper Alex Meret.
Diaz doubled the lead eight minutes later when he received a cross inside the box, threw a dummy that left Napoli defender Mario Rui stranded and sent the ball into the net with a deflection.
Milan effectively ended the match 14 minutes into the second half when Leao ran into the box, twisted and turned past three Napoli defenders and lashed his shot in.
Alexis Saelemaekers scored a fourth after 67 minutes with a solo effort in which he went past four defenders before putting the ball through Meret’s legs.
It was the first time in more than 22 years that Napoli have lost a Serie A match at home by four or more goals.
