Agostino Mazzoni was born on March 12, 1935 in Rome, Italy. He started his soccer career with the famous Lazio youth team. He then moved to Virtus Spoleto.

He played for Parma in Serie B in the 1957-1958 and 1958-1959 seasons.

In April 1959 Agostino signed for Montreal Cantalia. He was supposed to arrive in Montreal on Saturday morning April 11, 1959 together with five other players from Italy. This led to huge stress for Cantalia’s president Ernie Stastny and coach Skander Perolli. After the mix-up, the half-dozen of Italian soccer stars arrived at Dorval Airport in Montreal on Thurday April 16.

Agostino was described as a two-footed type of player. As well as as starring in the 1959 National Soccer League season, Gus also was a key player for Montreal Cantalia in their exhibition games during the summer of 1959.

On June 10, 1959 he played against West Bromwich Albion. The English tourist won 4-0.

More than 7,000 soccer fans turned up at Stadio Fallion on June 25, 1959 when Cantalia played against Napoli of Italy. Napoli beat Cantalia 2-1.

A crowd of 4,500 watched Montreal Cantalia beat Deportivo Municipal Lima on July 7th, with Cantalia winning 1-0 against the Peruvian tourists.

Gus was a vital member of the Cantalia team that won the 1959 National Soccer League regular championship. In the playoff championship the Cantalia team lost to Toronto Italia in the finals.

He returned to Parma in Italy in September 1959 after his spell with Cantalia. However, he failed to break into the first team and was duly released.