SALZBURG, Austria — The curtain had just come down on Anna Netrebko’s highly anticipated debut as Verdi’s Aida here earlier this month. But her next performance was already beginning.

As the elegant Salzburg Festival audience filed out of the theater — the men in black tie and traditional Austrian jackets, the women in long gowns and dirndls — Ms. Netrebko was upstairs in her dressing room, changing out of her black wig, costume and makeup. When she emerged, she was blond and in a gala-ready black dress, and she made her way through a narrow hallway packed with well-wishers, managers, record company executives and fellow singers.

Plácido Domingo was waiting by the stage door to praise her performance as “perfection.” Ms. Netrebko paused to sign some autographs and pose for a few pictures and then left for the opening-night party in a nearby Baroque palace where Mozart, born just a few blocks away, once performed.

“Now I am blind!” Ms. Netrebko cried as she navigated a red carpet illuminated by television lights and paparazzi flashbulbs; her role debut was front-page news here, even in a local mass-market tabloid that had a picture of a topless woman inside. She swept into the gala through a side door, making her way through the palace kitchens, and took her seat in the glittering hall. There she joined the production’s conductor, Riccardo Muti; the rest of its cast and creative team; festival officials; and a table of leading Austrian industrialists for a late-night supper that began with selfies and dollops of caviar.