Caballé's international breakthrough came in 1965 when she replaced a pregnant Marilyn Horne in a semi-staged performance of Donizetti's "Lucrezia Borgia" at New York's Carnegie Hall, which earned her a 25-minute standing ovation. While this was her first engagement in a bel canto opera and she had to learn the role in less than one month, her performance made her famous throughout the opera world. Later that year, Caballé made her debut at the Glyndebourne Festival singing her first Marschallin in Richard Strauss' "Der Rosenkavalier" and portraying the role of Countess Almaviva in Mozart's "Le nozze di Figaro".