In 1921, at age 17, he made his Berlin debut performing in Busch's ensemble as the keyboard soloist in the Brandenburg Concerto No. 5. At the end of the concert, Busch told Serkin to play an encore to the enthusiastic audience. Serkin later reported that he asked Busch, "What shall I play?" and Busch "as a joke" told him to play the Goldberg Variations "and I took him seriously. When I finished there were only four people left: Adolf Busch, Artur Schnabel, Alfred Einstein and me."