BBC Symphony Orchestra / Runnicles, Barbican Hall, London

Tristan and Isolde drink the fateful love potion, their passions runneth over, and, in a volley of brass fanfares, the figure of King Mark is seen awaiting his bride. But we now have to wait until February for Acts II and III of Wagner's seminal music drama – which is a hiatus for those of us who know the piece intimately, and something of a black hole for those who don't. Dramatic continuity goes straight to the four winds, as do all those crucial thematic relationships. Why? Why serialise, and, in so doing, diminish one of the single most influential works in the entire repertoire?

Well, seemingly for that very reason: to demonstrate its influence. The long list of works that might not have been possible but for Tristan und Isolde continues to grow even now. So, for this three-concert series from the BBC Symphony under Donald Runnicles, each act is prefaced by another work with a subliminal or direct relationship to it. Act I was preceded by the "symphonic fragments" from Debussy's Le Martyre de Saint Sébastien, in which music of abject chastity conceals quasi-religious passions of a deeply sexual, indeed sado-masochistic, nature. Runnicles and the BBC Symphony were coolly poised. It was a bit like receiving absolution in advance of the sin.

Then came the questing opening bar of the Tristan prelude, culminating in the most ambiguous and talked-about chord in musical history. Runnicles slowly, inexorably, built the prelude to a heated climax, his strings really using the whole length of the bow for a change, fortissimo horns repeating the initial question over and over but getting only a potent silence in response. That silence, broken only by the expectant murmur of cellos, typified the extraordinarily theatrical atmosphere of this concert performance. The beautifully distanced voice of the lone sailor (Mark le Brocq) really did sound caught on the wind. And from that comes the visual sense of an open sea and land on the horizon. So what point the paltry (and now seemingly obligatory) light show? Wagner's very own lighting cues are all but written into his heady score.

The casting here would grace any international opera house. But perhaps Christine Brewer's exceptional Isolde sounds the way it does because she chooses largely to steer clear of the international opera circuit. Here's a singer who really knows her voice and always sings within it. She truly rode the tempest of the opening scene; the curse on Tristan was formidably weighted, as was her imperious enunciation of her own name, the final syllable dropping intimidatingly into the chest voice; and yet there was great poise and beauty, too. The marvellous moment when she recalls how Tristan looked into her eyes invoking compassion where she had felt only hatred was but one memorable instance.

I can't wait to hear John Treleaven's Tristan in Acts II and III. This excellent singer seems to have reinvented himself as a fully-fledged Heldentenor(and don't we need them badly): the voice has truly marinated, acquired the darker colorations and the girth. But on drinking the love potion, he can still give us the most honeyed and perfectly placed "Isolde" – the name held in timeless rapture.

Add to these distinctive voices, the equally distinctive and very feisty Brangane of Dagmar Peck-ova, and a promising young Israeli baritone Boaz Daniel as Kurwenal (a lean, hungry, well-produced voice, this) and you've a pretty flawless cast. Of course, neither Tristan nor Isolde has to contend with the stamina issues of a complete performance. Perhaps that was another consideration in making us wait two months for the rest.

Act 2 will be performed on 5 Feb, Act 3 on 19 Feb (020-7638 8891)