It is always a pleasure to see a superstar at the top of his game in a relaxed, unbuttoned performance. Bryn Terfel, the phenomenal Welsh baritone, occupies the same rarefied firmament as Domingo, Kissin, Ma and Fleming, and a packed Kennedy Center Opera House hung on his every note and word on Saturday evening, in a program of arias and show tunes with Placido Domingo himself conducting.

Terfel is by now perfectly at ease onstage, making frequent eye contact with audience members while singing and between selections. He bantered with us, sharing anecdotes about his border collies, lamenting how it took him a year to learn “Die Walkure,” calling for us to whistle with him at the end of one number, and fetching a rose offstage to present to his duet partner, Ana Maria Martinez (a last-minute replacement). His stage business during “Udite, udite,” from Donizetti’s “L’Elisir d’Amore,” included what very much appeared to be drinking beer — and this was the opening number! His seductive moves on Martinez in Mozart’s “La ci darem” gave one chills to watch.

Terfel appeared trimmer than he has in the past, but his voice remains the same astounding instrument that set the world afire in 1989, when he won his first major international competition. It is in the extremes — high, low, loud, soft — that his natural gifts most clearly set him apart from others; the sound pours out like warm honey without any sense of strain.

The only noticeable issue is when he is singing full out in his lower register, at which point the tone can become a little wobbly. But he is an astute, thinking artist who never bellows. He knows exactly how to sculpt the sound for each character, each phrase; whether in the shape of the mouth, the placement between the head or chest, or the snap of the consonant (though as to the latter, while his diction is crystal clear, it cannot be said that he sounds like a native Italian or German). At this point in Terfel’s career, every performance is a master class in singing and stagecraft.

Martinez delivered a lovely, understated “Vissi d’arte” from “Tosca” and a spectacular final note in “Bess, You Is My Woman Now” from “Porgy and Bess.” Domingo’s conducting continues to unimpress. While his hand was relatively sure in the numbers he knew from his own repertoire, the difficult “L’onore!” from Verdi’s “Falstaff” was a mess; he repeatedly allowed the orchestra to swamp Terfel in the show tunes; and he could not find the Viennese lilt in Strauss’s “Die Fledermaus” overture. The Opera House Orchestra is playing well these days, but not always well enough to cover for weak conductors.

Future one-off performances in this Domingo Celebrity Series will include Angela Gheorghiu and Deborah Voigt, both in March 2012.

Battey is a freelance writer.