You never know who might be in the audience.

Mezzo-soprano Suzanne Mentzer, who performs tonight at Aspen’s Harris Concert Hall, caught a fortuitous ear at one point in her now-dual career as a performer and teacher. And the rest, as they say, is history.

Mentzer came to the Aspen Music Festival and School as a student in 1976, after her sophomore year at University of the Pacific in California. Then she decided to take a risk, leaving California for the Juilliard School, where, Menzer says, she “did OK, but didn’t stand out.”

Nonetheless, it was a Julliard that she participated in a televised master class with famed tenor Luciano Pavarotti. And a few years later — when she was burned out on singing and was taking time away from it — Mentzer received a call out of the blue from a manager at Columbia Records. He had seen her when he was watching that master class, and he asked her if she was still singing.

"I was so lucky," Mentzer said. "He would take chances on young singers, and he got me a lot of work without me ever singing. My career took off extraordinarily fast."

She found herself working hard under pressure to hold her own with older and more experienced artists — singers like Joan Sutherland, with whom she performed and recorded Gaetano Donizetti's “Anna Bolena,” playing Jane Seymour to Sutherland’s Anne Boleyn. She has performed with Frederica Von Stade, Marilyn Horne, Samuel Ramey and Placido Domingo, beside whom she played "trouser" roles (when women play young men or boys) for “Tales of Hoffman” and “Idomeneo.”

In 1999, she returned to the Aspen Music Festival and School to sing, and was asked if she was interested in teaching in Aspen.

"I said, 'Heck yeah!,' " Mentzer recalled. Currently, she also teaches at DePaul University, though she is about to move on to the Shepherd School of Music at Rice University. "I never thought I would teach," she said. "But I started giving master classes and really got into it. I realized I did know something."

Juggling teaching and performance careers is challenging, Mentzer admitted, but she excels at both, as evidenced in the variety of her performances at the festival this season, in addition to her work with students. She was a featured soloist in the festival’s season benefit, "The Ninth on the Ninth: A Beethoven Celebration," and in several chamber music concerts.

Tonight at Harris Concert Hall (8 p.m.), Mentzer presents a recital with Craig Rutenberg on the piano. Among the selections on the program is the world premiere of Libby Larsen's “Sifting Through the Ruins,” written for Mentzer and violist James Dunham. In fact, the text came out of Mentzer's own notes, taken at a New York Historical Society exhibit of tributes written to the victims of the 9/11 terrorist attacks, which she sent on to Larsen.

"They were very moving, even uplifting in some ways," Mentzer said. "[Larsen's music] is very simple, with a lot of emotion in the viola, but more detached in the voice. My part is almost that of a narrator."

Mentzer performs in concert often now, as her career continues to take her through American university campuses, recording studios and major European opera houses.

"I like concert work because you have more control over the repertoire," she says. "You have greater collaboration with instruments, and are able to collaborate with great musicians."

Tickets for tonight’s performance are $42; they are available at the Wheeler Box Office, the gondola building box office and at Harris Concert Hall.