AC Milan overcame a struggling Lazio 2-0 on Saturday to provisionally take top spot in Serie A, while Victor Osimhen came off the bench for Napoli and scored in a 4-0 win at Lecce.
Christian Pulisic gave Milan the lead on the hour at the San Siro when he slammed in a bobbling pass from Rafael Leao for his third goal since joining from Chelsea.
Leao was again involved as Milan made sure of the points in the 88th minute, the Portugal winger bursting into the area before cutting the ball back for Noah Okafor to slide home.
Milan's sixth win in seven matches pushed them three points clear of city rivals Inter, who can reclaim top spot by beating winless Salernitana later on Saturday.
France goalkeeper Mike Maignan returned for Milan after missing the past two games with a thigh injury he sustained in a goalless draw against Newcastle in the Champions League.
Lazio suffered their fourth defeat of the season and dropped to 14th place, with just seven points from as many matches.
Napoli secured their second victory in four days as the Italian champions climbed up to third.
After a run of three games without a win, Rudi Garcia's side have rediscovered some form heading into next week's Champions League clash at home to Real Madrid.
Centre-back Leo Ostigard headed Napoli ahead early on with his first league goal for the club, but it wasn't until the half-time introduction of Osimhen that the visitors took control of the game.
The Nigerian nodded in a cross from Khvicha Kvaratskhelia on 51 minutes before late goals from Gianluca Gaetano and Matteo Politano sealed the rout.
Politano struck from the spot as Osimhen left penalty duties to a team-mate for the second game running after the club posted a video online mocking him for a missed attempt.
Napoli said earlier this week they never meant to offend Osimhen after the player's agent threatened legal action.
Napoli moved to within a point of Inter but still trail leaders Milan by four points.
"It was a well managed match from start to finish, we wanted to hit hard and score in the first 15 minutes," said Garcia.
"I'm happy for Ostigard who is really a player who's constantly thinking about the team."
"We drew lessons from what happened in Genoa (a 2-2 draw on September 16), it's something that really pleases me," added Garcia.
"All our players are getting back to their best level, that's why the team is now finding this consistency."
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