Zlatan Ibrahimovic maintained his scoring run with a goal in each half to help Milan earn a 3-1 win over 10-man Napoli that takes his side back to the top of Serie A.
Sassuolo moved to the summit earlier on Sunday with a 2-0 win at Hellas Verona but Milan responded with an Ibrahimovic-inspired victory at Stadio San Paolo to go two points clear.
The veteran striker headed in from 14 yards with 20 minutes played to score for the eighth league game running before kneeing in an unorthodox second after 54 minutes, but he worryingly limped off late on with a thigh injury.
Dries Mertens had responded for Napoli only for Tiemoue Bakayoko to be sent off 165 seconds later and Milan, without head coach Stefano Pioli and a number of other backroom staff members due to coronavirus, wrapped up the win through Jens Petter Hauge's debut Serie A goal in injury time to maintain their unbeaten start.
Returning Napoli keeper Alex Meret pushed Hakan Calhanoglu's shot past the post and Simon Kjaer shinned wide from the resulting corner as Milan made a positive start.
The visitors did not have to wait long to make the breakthrough as Ibrahimovic got in front of Kalidou Koulibaly and headed Theo Hernandez's left-sided cross away from Meret.
Gianluigi Donnarumma produced fine saves to deny Dries Mertens and Hirving Lozano, either side of Giovanni Di Lorenzo firing against the crossbar, as Napoli initially responded well.
Those missed chances for Napoli would prove costly as Ibrahimovic converted Ante Rebic's floated delivery from underneath the crossbar to give his side some breathing space.
Ibrahimovic had an instant third rightly ruled out for offside and Napoli gave themselves hope when Mertens turned Alessio Romagnoli and beat Donnarumma with his shot.
But a clumsy challenge from Bakayoko on Theo saw the ex-Milan midfielder pick up a second yellow and Napoli failed to create any more clear-cut openings.
Ibrahimovic pulled up in what will be a big concern for the absent Pioli but substitute Hauge squeezed a shot past Meret from a tight angle to seal the three points.