 During that time, he made 111 appearances for the club in all competitions, scored one goal, and won the 2010–11 Serie A title as the team's starting left back.Antonini started his career at Milan, originally as a winger, playing for 11 years in their youth teams.At the start of the 2001–02 season, he was loaned out to Serie C2 side Prato, where he made his professional debut, totalling 26 appearances and scoring 3 goals.