The Italy international has been impressed with the forward's displays at San Siro since his January arrival
The forward arrived at San Siro from Manchester City in the January transfer window and has become an instant-hit with 11 goals as the Rossoneri have turned their campaign around since the turn of the year.
And though much was expected of the Italy international upon his arrival, Antonini admits he has been surprised at just how well Balotelli has performed.
"I expected him to be strong, but not this much," he told Sky Sport Italia.
"He is playing with purpose on the pitch and has 11 goals. He's integrated into a large dressing room and has been very positive - Milan have done very well to get him."
The full-back was also wholesome in his assessment of Stephan El Shaarawy's season and though the 20-year-old has struggled for consistency in the second-half of this term, Antonini is confident he will soon return to his brilliant best.
"Stephan has had a sensational year," he continued.
"He has struggled physically recently, maybe, but that should not tarnish his whole season. At 20-years-old he has been excellent and I am sure his form will return for the Confederations Cup."
The 30-year-old then committed his future to Milan by insisting he wants to "finish his career" at the club he has supported as a boy - despite not always being central to coach Massimiliano Allegri's plans.
"To be part of this club is a a source of immense pride for me and it's an honour for me to wear this shirt," he said.
"I had an injury which kept me out for a couple of months and other players got the chance to play, but I have been professional and accept the choices of the coach and will continue to be professional."
Milan are on course to clinch Champions League football for next season as they sit in third spot in Serie A with just two games of the campaign remaining.