San Antonio Missions
In 1933, Mazzera began his professional baseball career playing for the C-level San Antonio Missions. That year, Mazzera also played for the Baton Rouge Solons of the Dixie League, recording a combined batting average of .320 in 124 games played. Mazzera continued his minor-league career in 1934, playing for both the Palestine Pals of Palestine, Texas, and the San Antonio Missions. In 1935, Mazzera participated in 154 games for the San Antonio Missions while making his Major League debut for the St. Louis Browns on September 9, 1935. For his debut, Mazzera replaced Ed Coleman as a pinch runner.