Milan were held to a 1-1 draw by Sassuolo in the sixth round of the Italian championship after failing to protect their advantage.
Neither side could break the deadlock before half-time, despite both teams creating opportunities in an evenly contested opening period.
Milan eventually turned their superiority into a goal in the 63rd minute. Adrien Rabiot finished from a pass by Luka Modric to put the visitors 1-0 ahead.
Their lead lasted only five minutes, however. Cas Odenthal equalised for Sassuolo in the 68th minute, quickly taking advantage of the opportunity to bring the hosts level.
Both teams continued to compete for a winning goal, but neither could find another breakthrough and the match ended in a draw.