But that was the last sign of any weakness on the program. Starting with the Prelude and “Liebestod” from Tristan und Isolde, the orchestra found its feet and Runnicles caught fire. Christine Brewer gave a spectacular account of the soprano solo, her tone simultaneously rich and brilliant, soaring in a long line over the orchestra.

After the intermission, the audience was treated to about an hour of duets from Die Walküre. Nina Stemme and Christopher Ventris, passionate, convincing, and vocally outstanding Wälsung twins, sang the conclusion of Act I, starting with Siegmund's “Winterstürme.” The only possible improvement would have been if, in the depths of the love duet, they had managed to look at each other and sing to each other from time to time, instead of to the audience.

They were followed by Uusitalo and Brewer in the Act III Brünnhilde/Wotan duet, from “War es so schmählich” to the concluding “Magic Fire” music. Everything came together for a riveting performance, from the propulsive and grandly paced conducting to the musical and verbal interplay between Uusitalo and Brewer. She was, equally, noble, proud, and humbled by her situation; she gave meaning to every last word and shape to every phrase. She is a glorious singer and should be the Isolde and Brünnhilde of choice everywhere. Uusitalo brought tremendous sensitivity and plenty of authority to Wotan's music without a trace of bluster; he, too, is an intelligent singer always alive to the words. (With the addition of, say, Stephen Milling's Hunding and Stephanie Blythe's Fricka, San Francisco could hear a great Walküre – so what is the Opera waiting for?)

Where to go after Wotan's “Leb'wohl,” the heart-rending conclusion of Walküre? On to a perfect light dessert, of course, provided by Vaness and von Stade, who both sang signature arias. Vaness led off with a fiery, if somewhat thin-voiced, account Elettra's “D'Oreste, d'Aiace,” from Mozart's Idomeno. This is a classic rage aria, performed this time with a hilarious twist: at the first mention of snakes, Vaness casually whipped out from under the conductor's podium a six-foot, bright green, plush toy snake. She's a brilliant comedienne – please, cast her in a comic opera some day! Von Stade's “Tu n'est pas beau, tu n'est pas riche” (“You are not handsome, you are not rich”), from La Périchole, was funny and sweet, sung directly to Runnicles, who glowered and glared back at her – until she switched, mid-aria, to English, for a quick birthday tribute.

The evening closed – almost – with a spoken appreciation by Pamela Rosenberg and the appropriately serious presentation by British Consul General Martin Uden, on behalf of Queen Elizabeth, of the Insignia of the Order of the Most Excellent Order of the British Empire (OBE) to Runnicles.

But there was one surprise yet to come: stagehands wheeled out a giant cake, festooned with electric candles, and out leaped…..Carol Vaness, in a clingy dress and blonde wig, to sing a husky, sexy “Happy Birthday” to the Maestro. The whole audience and all of the solo singers joined in; flashbulbs popped; Runnicles said a few words of appreciation, and all went home happy with the evening and grateful for all that Donald Runnicles brings to the San Francisco Opera.