Zlatan Ibrahimovic made his second straight match from the start in Milan and had good memories from the last.
Then the striker accounted for both goals in the 2-0 victory against Cagliari.
But the home match against Atalanta was something completely different and a real slap in the face.
Christian Romero made it 1-0 in the 26th minute, which was the only goal of the first half.
In the second half, both came 2-0 on penalties by striker Josip Ilicic and 3-0 by Duvan Zapata.
Milan leads Serie A while Atalanta is fourth.