France forward Mbappé broke the deadlock with a clever low shot before the break, before Kolo Muani doubled the advantage in the second half after some fine play by their national team partner Ousmane Dembele.
Lee Kang-in added a third in the last minute for good measure. While it was not an easy affair in the first half, Luis Enrique's side prevailed to be on six points from three games, two ahead of Borussia Dortmund who claimed a 1-0 win at Newcastle United.
AC Milan, who have now failed to score in five consecutive Champions League games and netted only once in their last four competitive matches, are bottom of the group on two points. (Reuters) Daily newsletterReceive essential international news every morning Take international news everywhere with you!