Milan lost their 100 percent record as they were held to a 0-0 draw at Livorno.
The Rossoneri created the better chances throughout the game, and were particularly dominant in the first half as Kaka and Filippo Inzaghi both went close.
Livorno almost took the lead against the run of play when Cristiano Lucarelli blazed over from inside the area.
Stefano Morrone also struck the crossbar for Livorno as the home side's confidence grew in the second half.
It was Milan who had the last opportunity to snatch victory, but keeper Marco Amelia did brilliantly to pluck the ball away from Ricardo Oliveira five minutes from time.
Milan, who won their opening three games in Serie A, remain in the bottom half of the table after starting the season with an eight-point penalty.
In the evening game, Messina missed the chance to go top, as Catania held them to a 2-2 draw.
Sergio Floccari fired Messina in front (32), before goals in quick succession from Giuseppe Mascari (57) and Gionatha Spinesi (60) put Catania in charge.
Their lead was short-lived though, as Nicolas Cordova levelled for Messina just three minutes later.