Complex sentence: At his debut in Hamburg in 1889, he played Tchaikovsky's Piano Concerto No 1 in B flat minor with the composer conducting, this concert was a great success and determinant for his beginning career as a concert pianist in Western Europe.
Split into simpler sentences: At his debut in Hamburg in 1889, he played Tchaikovsky's Piano Concerto No 1 in B flat minor with the composer conducting. This concert was a great success and a catalyst for his budding career as a concert pianist in Western Europe.