Giacomazzi rose the ranks quickly having in one year gone from Serie D to Inter in Serie A, where he remained for eight seasons. A classic player, he was known for his humility, dedication, and work-rate. Strong, bold, and determined in only a year he earned the starting spot and the club's #3 shirt. Soon he formed the central part of a defence which was strong enough to help the team win two championships (in 1953 and 1954) and earn a call up to the national team. As a veteran player, he went to Alessandria where he played three seasons in Serie A and four in Serie B along with a talented youngster in Gianni Rivera.