Mazali, a member of the Nacional side that won three consecutive domestic titles between 1922 and 1924 (the side only conceded 29 goals in those three, turbulent seasons; Peñarol were banned from the national league in 1923), made his debut on 26 May 1924 in an Olympic Games fixture against Yugoslavia in Colombes, Paris, having won his place from Pedro Casella who, at the time, was plying his trade with Rampla Juniors. Uruguay won that fixture 7–0 and he conceded only two goals on his way to the Olympic title. By the time of the 1924 South American Championship his place behind his captain José Nasazzi was assured, where he conceded only one goal on his way to achieving victory with Uruguay.