While Milan's weekend game was postponed due to hazardous weather in Bologna, the league leaders posted a third straight win to move eight points clear of their Rossoneri rivals.
Match preview
Milan ultimately sat out the weekend action due to their fixture with Bologna being called off on Friday, due to recent flooding in the Emilia-Romagna region.
Safety concerns saw Lega Serie A decide to postpone the game, and a new date will soon be confirmed: February has been suggested, because both clubs are involved in either the Coppa Italia or Champions League.
In the latter competition, Milan finally got off the mark with a win over Club Brugge last week, reviving an ailing campaign by beating the 10-man Belgian side at San Siro.
The seven-time European champions led when Christian Pulisic scored direct from a corner, before their visitors had a player sent off and later equalised against the odds; two clinical strikes from Tijjani Reijnders then turned the game in Milan's favour.
That brought some redemption for Reijnders, who had seen red in the Rossoneri's most recent league outing, when they were forced to defend Samu Chukwueze's early goal while playing for over an hour with 10 men.
Having bravely seen off Udinese, Paulo Fonseca's side kept themselves within range of the Serie A pace-setters, led by this Tuesday's opponents.
The teams' most recent meeting saw Milan edge a one-goal game in February; so, including a 2-2 draw down in Naples this time last year, they are five games unbeaten against Napoli across all competitions.
During that winless streak, Napoli were knocked out of the Champions League by Milan in an otherwise successful 2022-23 campaign that saw them replace the second-city giants as Italian champions.
Much water has travelled under the bridge since then, but the Campanian club now seem to have found a worthy successor to Scudetto-winning coach Luciano Spalletti, as Antonio Conte is working wonders in Naples.
With help from a generous transfer budget by modern Serie A standards, Conte has clearly transformed a squad that toiled last term and failed to even secure European qualification.
Much fancied for the Milan job when it became apparent that Stefano Pioli would be leaving, fate conspired to take him to Stadio Maradona instead, and his new team lead the pack after nine matches.
Napoli tightened their grip on top spot at the weekend, when they saw off lowly Lecce by virtue of a second-half strike from captain Giovanni Di Lorenzo.
In the process of keeping a clean sheet in six of their last seven matches - including victory over Palermo in the Coppa Italia - Napoli have recorded an aggregate scoreline of 16-1 in their favour, serving notice they can challenge Juventus and both Milan clubs for the title.
AC Milan Serie A form:
D
W
W
W
L
W
AC Milan form (all competitions):
W
W
L
L
W
W
Napoli Serie A form:
W
D
W
W
W
W
Napoli form (all competitions):
D
W
W
W
W
W
Team News
Unable to serve one-match bans against Bologna, Milan duo Theo Hernandez and Reijnders will instead be suspended on Tuesday evening, so Filippo Terracciano should fill in at left-back, while Reijnders's replacement is uncertain.
Alvaro Morata leads the hosts' attack, supported by Christian Pulisic, who has been directly involved in at least one goal in each of his last seven league matches. Only one man has had a longer run for the Rossoneri since 2004: Zlatan Ibrahimovic posted a streak of 10 almost 14 years ago.
Long-term absentees Ismael Bennacer and Alessandro Florenzi are still unavailable, but Davide Calabria and Tammy Abraham could return to the bench following brief layoffs.
Meanwhile, Napoli rested first-choice wingers Khvicha Kvaratskhelia and Matteo Politano at the weekend, but both should be back in the starting XI at San Siro, with David Neres and Cyril Ngonge dropping out.
They will link up with Romelu Lukaku in the final third: with either a goal or an assist at his old home ground, the ex-Inter striker would reach 100 goal involvements in Serie A.
Midfield metronome Stanislav Lobotka has recently been sidelined by a thigh strain, but the Slovakia star could be back just in time to replace Billy Gilmour.
AC Milan possible starting lineup:
Maignan; Emerson, Tomori, Gabbia, Terracciano; Fofana, Loftus-Cheek; Chukwueze, Pulisic, Leao; Morata
Napoli possible starting lineup:
Meret; Di Lorenzo, Rrahmani, Buongiorno, Olivera; Anguissa, Lobotka; Politano, McTominay, Kvaratskhelia; Lukaku
We say: AC Milan 1-1 Napoli
Although Napoli look a more disciplined side than hit-and-miss Milan, the Rossoneri are particularly tough to beat on home turf.