Maybe the red dress made the difference.

In her U.S. recital debut Tuesday at the Perelman Theater, soprano Ailyn Perez was in somewhat uncertain form, seeming to fall into the trap of thinking more about the sound of her voice than about what she was saying with it. Even the best singers do that, but you hear it more with Perez because she typically establishes such a personal relationship with her audience.

Most such moments were in the first half of a mixed program of opera arias, art songs, and, as encores, pop standards. The Mozart aria "Dove sono" and Falla's Siete Canciones populares Espanolas had exceptional moments. But not until after intermission, having changed from demure black to blazing red, did Perez launch into the fearsome "Sempre Libera" aria from Verdi's La Traviata, going so far as to eclipse her best self.

This great soliloquy, sung by a character torn between love and pleasure, is expressed in all manner of vocal leaps, a certain percentage of which always go out of tune. One after another, Perez was spot-on - not in ways that felt well-drilled, but part of inhabiting the character in an equal fusion of musical and theatrical veracity.

The Philadelphia Chamber Music Society concert was originally announced as a joint recital with Perez's husband, tenor Stephen Costello, who canceled because of other commitments. But his family from Northeast Philadelphia, plus longtime fans from the Academy of Vocal Arts and Ocean City Pops, gave her a raucous welcome, sometimes applauding before the aria in hand was over, and eliciting from her some hometown gregariousness (though she's from Chicago).

It's sweet when somebody so outwardly glamorous is so attentive and motherly toward the audience. Certain songs prompted spoken introductions, when all she had to do was sing them with the emotional presence and text sensitivity apparent from her first student appearances here.

Her voice is evolving coloristically, with a lower range that is growing particularly rich. In a set of Fernando Obradors songs, she also achieved subtle vocal portamento, allowing her to float through the melodic lines while giving individual notes their proper due.

Often, her particularly original phrase readings seemed to be in response to something similarly astonishing from accompanist Ken Noda.

Encores included "Have Yourself a Merry Little Christmas." But at a certain point, does it matter what she sings?