Koulibaly started for his first minutes under manager Graham Potter on the night.
“We knew this was a difficult match against a great Milan side, who were in good shape. We absolutely wanted to win this game, I am also glad to be back on the pitch and hope it will go better in future," Koulibaly told Sky Italia.
“I am a player who needs to play regularly, everyone knows that. It is also true that I needed a period of adaptation, I am doing it well, I'm not perfect yet or what I want to be, but I'm getting there.
“I am very happy with this victory and the clean sheet, as it is always pleasing for a defender to not concede. We can be glad because Milan are a great team and we proved today that we could beat them.
“San Siro in a week will be a huge game, a massive stadium, Milan are very difficult to beat at home, but we will go there trying to get the three points and knowing Milan too will do everything to win."