Robinho had a great chance to give the hosts an early lead, but after being picked out unmarked at the back post, he side-footed a volley wide.
They came even closer soon after when Robinho played a low delivery into the box that was met by Bryan Cristante, but he saw his attempt come back off the bar.
Kaka was next to test the keeper when he fired in a low strike from the edge of the box that Consigli stretched out a hand to tip wide.
The Brazilian did not have to wait long for his next chance and finally broke the deadlock with his 100th goal for the club.
Urby Emanuelson played the ball through to Kaka, who took a touch before slotting a low strike past the keeper and into the bottom corner of the net.
In the final minute of the half Atalanta came close to snatching an equaliser when Cristian Raimondi fired a strike from outside the box that came crashing off the post.