The home side had two goals from Pato, one in the 30th minute and the second in the 41st minute. Atalanta would cut the lead in half in the 56th minute as Valdes scored in the 56th minute.
One more goal from Milan put the match out of reach as Ronaldinho missed a penalty but Marco Boriello was there to score on the rebound. They continue to trail Inter Milan by four points at the top of the Serie A table.
AC Milan 3-1 Atalanta Video Highlights
Pato 30′ (1-0), Pato 41′ (2-0), Valdez 56′ (2-1), Borriello 61′ (3-1)