Milan are second in Group H following their 3-0 win at Celtic Park and just need to avoid defeat at home to Ajax to reach the knockout stage of the tournament.
"Tonight's victory is extremely important regardless of our previous results," he told UEFA.com. "It is an essential victory and we achieved the result we wanted. I was not expecting it to be like this, but this shows the way we played. We worked hard to get a good result and in the end it was a fair score and we deserved it.
"We play at home, where we can get a good result. A victory or even a draw would be enough for us to qualify. This victory arrives at a good time and we needed a good result to improve our confidence. Every day I feel better, every game I feel better. I am happy with the way I'm playing and with the way things are going. I'm scoring lots of goals. I feel fine and I'm happy."
Kaka rejoined Milan from Real Madrid in the summer transfer window.