The Brazilian struck either side of half-time, after Mario Balotelli had given his side an early lead at the San Siro, to seal a second consecutive Serie A win.
It was a night to remember for Kaka, who was substituted to a standing ovation 15 minutes from time.
And the Brazilian could not hide his delight, telling Sky Sports Italia: "The goal means many things. It is a special moment for us, tonight was an important achievement for me to play 300 games and it went better than I could've expected. I am very happy."
Clarence Seedorf's men were the subject of much criticism last week, having not recorded a league win for five games.
But two consecutive wins have helped to ease some of the pressure on Milan, while also keeping their faint hopes of European qualification alive.
And Kaka insisted that despite a difficult campaign there are no problems in the dressing room.
"Football is wonderful and painful precisely because it changes so quickly," he said.
"I said last week our locker room was not divided and people could see that tonight.
"We had two wins and a draw now, so these are results that will help us to end the season on a high."
The 31-year old was also asked about his recent comments suggesting he would one day like to play in the MLS and responded: "I am happy here. Every time I am at Milan, people only want to talk about my future."
