Defender Gabbia rose highest to thump home Tijjani Reijnders' free-kick in the 89th minute and give Milan a Serie A win which pulls them out of a miserable early season slump.
Juventus were held to a 0-0 Serie A draw at Empoli on Saturday as Thiago Motta's side dropped more points after their goalless home stalemate against AS Roma before the international break.
Inter and AC Milan on Friday rejected the project to modernise and restructure the iconic San Siro stadium which they share, city mayor Giuseppe Sala announced.
Victor Osimhen has been sidelined by Napoli after the team he fired to Serie A glory just a over year ago left him both off their squad list for the 2024/25 campaign and potentially in season-long limbo.
Belgium striker Lukaku completed a permanent move to Napoli from Chelsea on Thursday, ending a long period of limbo with the Blues.
Inter Milan thrashed Atalanta 4-0 on Friday to move provisionally top of Serie A, while Torino snatched a late 1-0 win at Venezia to continue their positive start to the campaign.
The futures of Napoli striker Victor Osimhen and England international Ivan Toney are set to dominate the final day of the European transfer window on Friday as Chelsea continue their frenzied pursuit of new signings.
Napoli have signed Romelu Lukaku from Chelsea, the Serie A club announced on Thursday, ending the Belgium striker's extended period in limbo with the Blues.
Poland goalkeeper Wojciech Szczesny on Tuesday announced he was retiring from football at the age of 34 less than two weeks after the end of his contract with Juventus.
Lautaro Martinez ensured that Inter Milan kept hold of their two-point lead at the top of Serie A as he struck in Sunday's scrappy 1-1 draw at closest rivals Juventus.
AC Milan starlet Francesco Camarda made history on Saturday after becoming the youngest ever player to play in Serie A during Saturday's 1-0 win over Fiorentina.
Mazzarri's team are still seven points behind leaders Inter Milan who travel to Turin on Sunday for the weekend's big match at second-placed Juventus
Inter Milan and Juventus face off on Sunday in a clash between Serie A's two title favourites and historic rivals, as Walter Mazzarri begins his second reign at troubled Napoli.
Napoli continued their struggles on home turf with Sunday's shock 1-0 defeat to Empoli which left the Serie A champions already well off the pace in this season's title race.
Napoli winger Matteo Politano and forward Giacomo Raspadori both scored after the break to cancel out two first-half headers by Olivier Giroud in an energetic game that saw the two teams dominate one half each.
Argentina striker Martinez nodded home his 11th league goal of the season in the 67th minute of a straightforward win in Turin as Inter went one point ahead of AC Milan, who host third-placed Juventus on Sunday night.
Italian club Juventus' midfielder Nicolo Fagioli is under investigation for alleged illegal betting activities, a prosecutor said on Wednesday, confirming earlier press reports.
Bologna fought back from two goals down to snatch a 2-2 draw with Inter Milan at the San Siro in Serie A on Saturday after early goals from Francesco Acerbi and captain Lautaro Martinez had put the hosts in command.
Lukaku grabbed his third goal in five league games for Roma after latching onto a clever pass from Paulo Dybala midway through the first half.