It was a blockbuster concert, a box-office sure thing: the soprano Deborah Voigt and the tenor Ben Heppner, singing arias and duets. What arias and duets? German ones, of course, for Miss Voigt and Mr. Heppner are two of the most celebrated “German” singers – Wagner singers, more specifically – in the world. (She is an American, he a Canadian.) The concert took place on Wednesday night at Avery Fisher Hall, and the singers’ backup band was the Orchestra of St. Luke’s, conducted by Asher Fisch, an Israeli who is particularly known for opera.

Miss Voigt first sang the aria from Beethoven’s “Fidelio,” “Abscheulicher … Komm, Hoffnung.” She was in good voice, showing her famous combination of power and lyricism. Her vibrato seems greater than it used to be, and sometimes a stridency wants to steal in – but she is still La Voigt. Unsurprisingly, she shaped the aria intelligently. And when she sang “Komm, Hoffnung” – “Come, hope” – she did so with wonderful warmth. This was, indeed, an earnest invitation.

Nice about this soprano is that her lower register is audible – you get used to not hearing the low notes, through the orchestra, in this aria! Unfortunately, she was majorly flat on her big high B.

Then Mr. Heppner appeared, for his first aria: “Nein, langer trag’ ich nicht die Qualen … Durch die Walder,” from Weber’s underperformed opera “Der Freischutz.” He, too, was in good voice, exerting a minimum of strain, although with that pinchedness he sometimes fights. Maestro Fisch and the orchestra were guilty of covering him now and then. But Mr. Heppner was convincing in this aria, rendering it with dramatic potency.

And to conclude the first half of the concert? The granddaddy of all love duets, that from Wagner’s “Tristan und Isolde.” If both singers did their best – or somewhere close to it – this would be a treat.

The duet didn’t start promisingly, with both singers flat – in Mr. Heppner’s case, painfully so. It should go without saying that Miss Voigt and Mr. Heppner did some things well as the music progressed. For example, the soprano’s singing of “Lausch, Geliebter!” (“Listen, love!”) was truly touching; the tenor’s response – “Lass mich sterben!” (“Let me die!”) – was almost equally so. But the duet did not breathe as naturally, or as inevitably, as it should. This must be laid at the feet of Mr. Fisch. The kind of drunken momentum that this music should have did not kick in. On the whole, the duet was more sleepy than sensual, and Wagner’s fornicating bits seemed almost chaste. At the end, Miss Voigt was nowhere near her big high B.

Did the superstar singers enlist a Brangane? They did indeed. This was Margaret Jane Wray, issuing her warnings to Tristan and Isolde from some hidden spot in Avery Fisher Hall. She was impressive as Sieglinde in Wagner’s “Walkure” at the Metropolitan Opera last season, and she was impressive on Wednesday night: secure in tone, pitch, understanding – everything. Tristan and Isolde really had to be doped up not to heed her.

Miss Voigt opened the second half of the concert with her signature duet, “Dich, teure Halle,” from Wagner’s “Tannhauser.” Why do I say “signature”? Because she tends to sing it on big occasions – and smaller occasions – and she almost invariably sings it well. She did so on Wednesday night. In a slight diva move, she let the orchestra perform its initial music without her, entering in time to sing. For years, I – along with others – have described her singing as “refulgent”: “She sang refulgently,” “She poured forth her refulgence,” etc. Well, in “Dich, teure Halle,” she was refulgence itself.

But continuing my theme (and hers): She was a mile low on her high B. In fact, she did not have top notes all night long, which is not unworrisome for a soprano.

Then, Mr. Heppner, for one of his – or any Wagner tenor’s – signature arias: Walther’s Prize Song from Wagner’s “Meistersinger.” Mr. Heppner is an uneven singer, even in a field – i.e., singing – cursed with unevenness (or blessed, if you like the excitement or unpredictability of it). You never quite know what you’re going to get. And Mr. Heppner sang the daylights out of this aria. He was on the money, pouring out sound, and doing so on pitch.You want the Prize Song to be thrilling, and this time, you got it.

The duo ended with the final duet from Wagner’s “Siegfried.” Mr. Heppner has never been Siegfried on the stage, but that is coming (presumably). Miss Voigt has never been Brunnhilde on the stage – but that is coming, too (for sure). A singer commonly adds the heavier roles as he goes. This pair handled the “Siegfried” duet splendidly, and, though Miss Voigt failed on some early high notes, she sang a decent C at the end – a good time to do it.

The reader may wonder whether there were any purely orchestral items on the program: There were. Mr. Fisch and the St. Luke’s began the concert with the overture to “Fidelio,” which was somewhat labored and sloppy. More rehearsal would undoubtedly have helped. Horns were manful, however, as they would be in the Beethoven aria as well. And the final section of the overture can’t fail to excite – it is baked in, by Beethoven.

The orchestra made some really ugly sounds in the “Tristan” duet, particularly at the beginning. But Forest Murmurs,from “Siegfried” – which preceded that final duet – was positively beautiful. Startlingly so. Nothing the orchestra had done before had prepared us for this (believe me). Mr. Fisch conducted this wondrous excerpt superbly, and for a moment Avery Fisher Hall was Asher Fisch Hall (sorry).

Any encores? Just one. I was sort of hoping for the duet from Lehar’s “Merry Widow” – something lightish and charming to go out with – but Miss Voigt and Mr. Heppner took the Strauss song “Zueignung,” one of the most popular encores in the repertory. This is no duet, but the singers managed to make it one. The audience went crazy for this blockbuster pair, and they weren’t wrong.