In 1966 he left Dedé Wolff and the following year signed a five-year contract with the poet Horacio Ferrer with whom he composed the operetta "María de Buenos Aires", with lyrics by Ferrer. The work was premiered in May 1968 with the singer Amelita Baltar in the title role and introduced a new style of tango, Tango Canción (in English: Tango Song). Soon after this he began a relationship with Amelita Baltar. The following year he wrote "Balada para un loco" with lyrics by Ferrer which was premiered at the First Iberoamerican Music Festival with Amelita Baltar and Piazzolla himself conducting the orchestra. Piazzolla was awarded second prize and the composition would prove to be his first popular success.