 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.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.On 9 June 2008, Antonini was brought back by Milan and included in their squad for €2.75 million plus €150,000 other fee, in a pure player swap.