Just when it looked as though, after four tries, the Metropolitan Opera’s current revival of Wagner’s “Tristan und Isolde” would proceed on Tuesday evening with the originally announced cast intact, the nemesis that has dogged the run sprouted another hydra-like head. Ben Heppner, in voice and appearance the very image of good health, belatedly joined the cast as Tristan. But Deborah Voigt, the scheduled Isolde, canceled because of illness and was replaced by Janice Baird, who at an earlier performance took over for Ms. Voigt during the course of Act 2. The current “Tristan” problems, which have included not just sick principals but also staging mishaps, have at least afforded the Met the chance to hone its skills in coping with adversity, and it must be said that the company has responded magnificently. This was not one of those depressing affairs, where one singer sings from the pit while another acts the part onstage, or where a singer out of his or her league labors on to the end. It was a distinguished performance by any standard, including the Met’s own.

Mr. Heppner was in staggeringly good form. Nearly two weeks ago, the Met announced that he would be well enough to sing this performance (but not the one this past Saturday), and somehow called it right. Reportedly, Heppner might have been able to join the cast earlier but for a misdiagnosis of his malady. In any case, his Tristan remains a marvel. The voice has flexibility and stamina as well as lyricism, and Mr. Heppner brought a wealth of nuance to this many-faceted role. If there were one or two vocal blemishes in Tristan’s delirium scene, they seemed in character. And with Mr. Heppner’s current, relatively trim figure, he made a good match for Ms. Baird.

Ms. Baird, a dramatic soprano with notable credits in Europe, sang with gleaming, resonant tone and was a very feminine Isolde. Her voice may not have the voluminous dimensions on which Met audiences feed, but its size is more than adequate and, coupled with Ms. Baird’s interpretive and acting skills, made for a compelling portrayal. She maintained impressive control, for example, of the dialogue in which she persuades Tristan to join her in a suicide pact. Her lower range is not particularly strong, but she knows how to put across the low-lying phrases that count. Her singing was consistent, showing only the slightest signs of tiring in the Liebestod.

Michelle DeYoung (Brangäne), Richard Paul Fink (Kurwenal), and Matti Salminen (King Marke) are members of the fine supporting cast that has been stalwart though the various tribulations, and James Levine had the orchestra sounding in characteristically sumptuous form.