Young Spaniard Brahim Diaz opened the goals in the 24th minute after a pass from Zlatan Ibrahimovic.
Ibrahimovic himself had the opportunity to double the score in the 36th minute with a penalty kick, but he wasted it and hit the crossbar.
Milan did not stop in the second half, and scored again by Raphael Liao of Diogo Dalot in the 57th minute.
Dalot finished the goals himself in the 67th minute, after a pass by Algerian Ismail Bennacer.
Milan raised its score to 6 points at the top of Group H, while Sparta Prague stuck to 0 without any victory.
In another exciting match in the same group, French Lille tied at home to Celtic, Scotland, with two goals for each side at the Pierre Maury stadium.
Mohamed El-Youssi advanced to Celtic with two goals in the 28th and 32nd minutes. But Lille came back in the score by Zaki Celik and Jonathan Econe in the 67th and 75th minutes.
Lille raised his score to 4 points in second place, and Celtic collected his first points in the group.
In Group Nine, Villarreal, the Spaniard, overturned their delay in front of Azerbaijan’s Karabag to win 3-1 at Fatih Terim Stadium in Istanbul, Turkey.
Ghanaian Oso Kwabena stunned the visitors with a goal in the 78th minute.
Substitute Jeremy Pino tied for Villarreal directly in the 80th minute, 6 minutes after entering the pitch.
Before the other substitute, Paco Alcacer, takes over the rest of the task, scoring the second and third goals in the 85th and fifth minutes of injury time.
Villarreal raised its score to 6 points at the top of the group, and Karabag freezes at 0 points.