The latest chapter in the continuing drama of the Metropolitan Opera’s star-crossed “Tristan und Isolde” arrived on Saturday afternoon as Robert Dean Smith, an American tenor who has spent much of his recent career in Europe, became the third singer to take the role of Tristan in this run of six performances. Ben Heppner, originally scheduled for the entire run, is now listed on the Met’s Web site for only the final performances, on Tuesday and Friday. At this point even those seem dubious.

Mr. Smith, unlike his predecessors in this “Tristan,” John Mac Master and Gary Lehman, faced the prospect of making his Met debut in a performance that would be broadcast on radio and transmitted in high-definition video in movie theaters.

One performance, on March 14, was interrupted by the soprano Deborah Voigt’s sudden illness. In the next, Mr. Lehman was injured by a failure in a stage mechanism. Small wonder that there was an extra frisson of tension in the air on Saturday. Dramatic pauses in the prelude seemed weighted with portent, and at least one listener started slightly at an offstage crash and thump during the Steersman’s song.

Apart from that mystery noise and what seemed like a lighting miscue in the second act, the production held steady. Ms. Voigt set the tone for the performance with her clear, incisive and intelligent singing. The supporting cast followed suit, and the orchestra was sumptuous.

Mr. Smith’s greatest assets were his gorgeous tone and confident stage presence. He marshaled his resources with remarkable intelligence, sounding fresher and more engaged in the third act than he had in the first two. If much of his acting consisted of stock gestures, he did seem to have chemistry with Ms. Voigt.

But Mr. Smith’s voice could not match hers during more ardent passages in the second act. Nor did he have the heft and steel needed to cut through the orchestra at full cry. In a smaller theater he would have been a sensation, and he may well have made a greater impression in the broadcasts than he did in the house.

“Tristan und Isolde” repeats on Tuesday and Friday at the Met; (212) 362-6000, metopera.org.