After the tenor Juan Diego Flórez popped out his nine shining high C’s in “La Fille du Régiment” at the Metropolitan Opera on Monday night, the crowd rose and cheered. Mr. Flórez obliged with something not heard on the Met stage since 1994: a solo encore.

He sang the aria “Ah! Mes Amis” again, nailing the difficult note  a kind of tenor’s macho proving ground  nine more times. It was one of those thrilling moments that opera impresarios live for.

Image Juan Diego Flórez in Fille du Régiment at the Metropolitan Opera. Credit... Sara Krulwich/The New York Times

And, in this case, prepare for. Peter Gelb, the Met’s general manager, said on Tuesday that he had asked Mr. Flórez weeks ago whether he would be prepared to repeat the aria, if the audience demanded. Mr. Flórez had already done so at other houses, including the Teatro alla Scala in Milan, where last year he became the first to violate an encore ban since 1933.