AC Milan are currently winning Napoli 2:0 right now and if the match happens to end like this then they will end this week and this month of September on top of the Serie A standings. So far this this season they have been good that is why they are now sharing the same point with Napoli if they win. It should be a win for them because they have a two goal advantage over their opponent as it stands now. Napoli will need to score twice without response for them to grab a point tonight.
Milan managed to by win 2-1 in the end even though they had to play the whole second half with 10 players. They had 0 goal attempts after the red card by the way. Allegri still brought 3 points somehow.

Milan played with 10 players for a long time, of course, Napoli had enough chances to win. But they failed to take advantage of the opportunity, because they did not think that they would lose points so easily. This match was played with a lot of crazy attitude, Milan is a completely experienced team I think, but where 10 players have performed for a long time, the opposing team could certainly create a lot of pressure. But Napoli's attack has been very weak because their attack has seen a new look of players.
The game was a competitive one, while Milan had two early goals, Napoli was still fighting. The Milan defender dragged a Napoli player to stop an obvious goal and got a red card, the penalty was deserved one. By the looks of how game was progressive, even I thought Napoli would be dominant to a 10 men limited milan after the 60th minute but Napoli had over 30 minutes with 1 man advantage but failed to score a goal. They did tried but Milan defended.
With this win, there are three teams with exact 12 points leading the Serie A, Napoli, AC Milan and Roma while Juventus is just 1 points shy and the top position would be up for grabbing to any teams.