In his youth, Mazzoni played for Fiorentina, before playing for several other Tuscan teams such as Le Signe, Siena, and Empoli.[2]
After one season at Ascoli, he was bought by Bari for the 1953–54 IV Serie, where he spent most of his career, becoming the captain and reaching Serie A in 1958.[2] At Bari, he made a total of 313 appearances and scored 25 goals (of which 90 appearances and 7 goals in Serie A), becoming the third player with most appearances in the club's history.[1][7][4]
In 1970, Mazzoni was appointed as assistant coach of Fiorentina. At the end of the 1974–75 season, he replaced Nereo Rocco, who had quit his role of first team coach, leading the club to the victory of the 1974–75 Coppa Italia.[3] He also led Siena during the 1978–79 Serie C2.[5]