TORONTO – Tuesday, when Peter Sellars’ production of Wagner’s “Tristan und Isolde” opened at the Four Seasons Centre, expectations were high. No matter that the opera’s running time was five hours. The opera house was packed to the fifth tier.

A highlight takes place at the end of Act I, when King Marke arrives – creating a crisis for Tristan and Isolde, now under the influence of the love potion. The house lights went up, King Marke is in the aisle, and he and his henchmen are looking around at all of us as if wondering who is to blame. Wagner’s trumpets add to the shock and pageantry.

All the singers, garbed in brooding gray and black, were intense. What a thrill it was to hear Ben Heppner as Tristan. He projected easily, his strength a marvel, his diction a delight. Melanie Diener, as Isolde, was a great match for him – high praise for her. (On Feb. 8 and 23, two other singers star, Margaret Jane Wray and Michael Baba.) Daveda Karanas, with her smoky mezzo-soprano, brought a smoldering energy to the part of Brangaene, Isolde’s lady-in-waiting.

A surprise attraction was Alan Held as Tristan’s man Kurwenal. Kurwenal is often portrayed as youthful, but Held played a veteran soldier, tall and strong with a shaved head and a voice that demanded attention. He and Heppner could be seen sometimes as thugs, a touch that worked.

The images of video artist Bill Viola added another dimension.

The first act made me question their necessity. We kept seeing a man and a woman, dressed and then fully, frontally nude. The man looked nothing like Heppner. Who were these people?

In subsequent acts, though, things became clearer. Videos of waves crashing, the moon splashing through the trees, and a slow sunrise over a meadow gave a focal point to people unused to Wagner’s stream-of-consciousness writing.

One thing the video does particularly well: It solves the ancient problem of zaftig Wagner singers.

Diener, though far from petite, was lighted very well and carried herself with such grace that as the drama went on, she became beautiful. You could not say the same for Heppner. Wonderful as his voice is, he looked unprepossessing. Once, sparring with Melot (a handsome and resonant Ryan McKinny), the great tenor used his belly to push his adversary.

The video could correct this lack of romance. In the final Liebestod, Viola showed Tristan’s more slender video doppelganger rising from his casket, passing into the next world. Below the screen, Heppner himself virtually disappeared.

It was ingenious. It was also devastating. I was broadsided by it. Diener appeared like a ghost, like one who is already dead. She began the music in entrancing quiet, then built gradually to soaring heights.

When it was over, it took time to recover. The ravishing music, and the rawness and honesty of this production, added up to something overwhelming.

Sellars, in his program notes, is somewhat out there. Most outlandishly, he asserts that Tristan and King Marke had a homosexual relationship, a claim that has absolutely no basis. But he has clearly taken the opera to heart, and his sincerity showed in his work. ”

Pixyish in an orange ’70s shirt, Sellars joined the singers and conductor Johannes Debus in multiple curtain calls.