„Dreams have to come alive”
„Der Traumgörge”

Zemlinsky felt most at home in the genre of song and opera. If the sketch of the score of the late work Der König Kandaules is included, he completed a total of eight operas. Basically throughout his life Zemlinsky was searching for opera subjects. In addition to the completed works, nine fragments in various degrees of development and references to his reading of countless potential opera subjects testify to his permanent preoccupation with the genre. Zemlinsky wrote his first opera Sarema based on the dramatic poem Die Rose vom Kaukasus by Rudolf Gottschall; the libretto was probably written by his father or maybe he even wrote it himself.

He worked on Sarema from 1894 to 1895 which was awarded the Luitpold Prize by the Bavarian Prince Regent. Although it was stylistically still very inhibited, the opera already shows considerable dramatic talent. In 1897 even Gustav Mahler, newly appointed director of the Vienna Hofoper, expressed interest in Zemlinsky's first work. However, Zemlinsky offered him instead a new work of which the first few scenes already existed: Es war einmal, an opera based on a text by Maximilian Singer after a fairy-tale comedy by Holger Drachmann combining motifs from the Turandot fairy-tale and Shakespeare's Taming of the Shrew. Mahler accepted the opera and had it performed in January 1900 at the Hofoper — one of the most important events in the young Zemlinsky's career.

Zemlinsky's third opera Der Traumgörge (1904-06), in which he again set a fairy-tale subject (libretto: Leo Feld) to music, was also closely connected with Mahler as he had agreed to give it as a world premiere in the season 1907/08. However, before the premiere Mahler resigned his position at the Hofoper and his successor Felix Weingartner removed it from his plans without stating any reasons, even though it had been completely rehearsed. Among circles of the Viennese School the work was highly regarded but the world premiere did not take place until 1980 in Nuremberg. Zemlinsky suffered greatly from the fate of one of his most personal creations. Even at an advanced age, when he played through it on the piano he apparently said, „It is good”.