Antonio Conte’s Inter ended their 23-year wait for a league win in Naples to stay in pole position, level on points with Juventus after 18 games, but ahead on goal difference.
Romelu Lukaku helped Inter secure the historic win. He scored twice as Inter Milan held on to top spot in Serie A on Monday with a 3-1 win over Napoli to keep the pressure on Juventus who earlier swept past Cagliari with Cristiano Ronaldo netting his first hat-trick in the Italian top flight.
Lazio are third, six points adrift but with a game in hand, after stretching their winning run in the league to nine matches on Sunday with a 2-1 victory over Brescia.
“It’s an important victory, winning away to Napoli is never easy,” said Conte after his 100th Serie A win as a coach but first in Naples.
“Napoli have in recent years always been behind Juventus, while Inter was a long way back. This year we have reduced the gap.”
Inter’s three goals all came from mistakes from Napoli, runners-up the past two seasons but only eighth this term.
Lukaku broke through on 14 minutes with a powerful solo run through the Napoli defence, with goalkeeper Alex Meret fumbling the second into goal in the 33rd minute.
Polish striker Arkadiusz Milik pulled a goal back for Napoli four minutes before the break.
But Lautaro Martinez added the third after the hour mark, following another mix-up in the Napoli defence, to give Inter their first win at the Stadio San Paolo since October 1997.
“We made lots of mistakes and scored three goals on our own,” said Napoli coach Gennaro Gattuso.
“The lads are worried because they are used to challenging for the Scudetto and this year it’s like this.”