The draw, which from 22 minutes was played with 10 men for Milan, meant that they went through in second place from Group H behind Barcelona.
"When Ajax hit the post early on, I thought it was a good sign for us," he told UEFA.com. "I think all of us gave 100% tonight. We did not give them many chances, I think our qualification is fully deserved because we played some good games in the group and we lost only away to Barcelona.
"I think Mario Balotelli was very good in helping the team defend tonight. He did a great job. We will have to play with the same spirit in the round of 16."
Milan will now face one of the other group winners in the second round.