In January 1952 Rosenstock succeeded Laszlo Halász as General Director of the NYCO. He served in that post for four seasons, continuing Halász's innovative programming of unusual repertoire mixed with standard works. He notably led the world premiere of Aaron Copland's "The Tender Land", the New York premiere of William Walton's "Troilus and Cressida", and the United States premieres of Gottfried von Einem's "The Trial" and Béla Bartók's "Bluebeard's Castle". Rosenstock was also the first NYCO director to include musical theatre in the company's repertoire with a 1954 production of Jerome Kern and Oscar Hammerstein II's "Show Boat". This decision was ridiculed by the Press but Rosenstock felt justified as the production played to a packed house. Meanwhile, the company's production of Donizetti's opera "Don Pasquale" that season only sold 35 percent of the house seats.