During that time, he made 111 appearances for the club in all competitions, scored one goal, and won the 2010–11 Serie A as the team's starting left back.

[1] 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.

[8][9][10] With Empoli, Antonini made his debut in European competitions on 20 September 2007, in a UEFA Cup first-round game against Zürich, also scoring a penalty.

[11] Despite the team being relegated, he had an extremely good season, also showing versatility when coach Alberto Malesani started to employ him as a full-back.

[16][17] He finished his second year at Milan on a high, scoring his first goal for the Rossoneri in the last match of the season, a home game against Juventus, on 15 May 2010.

[18] When new coach Massimiliano Allegri was appointed in the summer of 2010, he kept Antonini at the left-back position and Luca was a regular in the starting XI for the whole of the 2010–11 season, helping Milan win their 18th Scudetto.

He continued to be a regular for the 2011–12 season, where Milan disappointingly finished second to Juventus but managed to win the Supercoppa Italiana in the summer of 2011.

At the start of the 2013–14 season, Antonini left Milan to join Genoa as part of a deal which saw midfielder Valter Birsa move the other way.

Nine years later, Antonini got his first call-up for the senior team; newly appointed coach Cesare Prandelli named him in the squad for a friendly against Ivory Coast, to be played on 10 August 2010.