known as a champion of contemporary music, masselos premiered many works including the charles ives piano sonata no. 1, the piano fantasy by aaron copland, and most of the piano literature by ben weber, including the concerto for piano and orchestra and the fantasy (variations), op. 25. he was the soloist in the first performances of piano concertos by alan hovhaness, johan franco, marga richter, carlos surinach, and william mayer, in addition to solo pieces by john cage, dane rudhyar, robert helps, carlos chávez, and many others.