Born in Hollenstein an der Ybbs, Telasko studied singing at the Wiener Musikakademie and at the Neues Wiener Konservatorium as well as musicology at the University of Vienna. He was a pupil of the baritone and singing teacher Viktor Fuchs (1888-1966) and made his debut as Heerrufer in Wagner's "Lohengrin" at the Volksoper Wien in 1934. From 1934, he was engaged for one season each at the Volksoper, the Vienna State Opera and the Stadttheater Troppau. In 1936 and 1937, he took over the role of Konrad Nachtigall in the legendary new production of "die Meistersinger" conducted by Arturo Toscanini at the Salzburg Festival, of which a complete recording is available. From 1937, he performed at the Opernhaus Graz and the Landestheater Linz, from 1938 he was also the director of the opera in Linz. After the Annexion of Austria by Hitler's Germany in March 1938, he was still allowed to perform as a half-Jew, but he must have been aware of the danger he was in. He also got a contract for the 1939/40 season, but used the theatre holidays in summer 1939 to escape, quasi at the last minute before the outbreak of World War II. He emigrated to South America via France, Spain and Portugal.