BBC SO / Runnicles, Barbican Hall, London

It's been three months since Tristan and Isolde drank the fateful love potion thus initiating the longest foreplay in history. Much was promised by Act 1 of the BBC Symphony's three-part "serialisation" of Wagner's masterpiece and perhaps it was regrettable that Act 2 couldn't pick up and build upon that impetus. The adrenalin rush at the end of Act 1 fuels the lovers' nocturnal tryst in the following act. Performers need to have come from somewhere to go somewhere. That's the way Wagner designed it. One act at a time means effectively starting again.

The concert started with Richard Strauss's Metamorphosen, which sat like a portent of Wagner's final act. To be logical, we should have been listening to it after Tristan had submitted to the blade of Melot's sword where the echo of King Mark's tragic music (a direct quotation on Strauss's part) will have been just that, an echo, not a premonition. Even so, it should have been moving if the performance had been half decent. Donald Runnicles rightly chose Strauss's original version for 23 solo strings but, frankly, there wasn't one solo player here of presence and profile enough to project the piece into a large auditorium.

Minutes into Act 2 of Tristan and the lovers are flying into each others arms, the music fizzing with excitement and expectation. The solo voices surf the orchestra; it doesn't matter one jot that you hear what they're saying, only that they are in a high state of abandon. John Treleaven (our Cornish Tristan – a happy coincidence) and Christine Brewer were both a little too score-bound to achieve that, and maybe Runnicles, too, was holding off the orchestra to give them every chance, but the whole passage didn't quite come off the page. And yet Runnicles had set up the act quite splendidly with dappled orchestral colourations sensitively etched and raucous hunting horns grittily medieval though way too close for comfort. No wonder Dagmar Peckova's excellent Brangane seemed more anxious than usual.

The real success of the evening, as had been the case in the first act, was Runnicles' sensitivity to atmosphere, to the sound of silence and stillness and the balmy rapture of the night so eloquently shared by his two leading players. Christine Brewer's Isolde was again close to ideal, not a single forced or ungenerous phrase. Treleaven was less free and slightly impeded in mezza voce by some dryness in the throat (it was a measure of his sensitivity that he moved out of his light to take sips of water). But what a pleasure to hear two singers who really form and fill their phrases mindful of cherishing them and whose words are in themselves music.

Peter Rose carried the burden of betrayal in King Mark's great monologue at the close of the act. But to sing it well, as Rose did, is not necessarily to see into his soul, which Rose didn't. That fell to Runnicles and a single note, a keening crescendo in the cor anglais that almost cannot bring itself to turn into the music of the king's inconsolable grief. He was a master, this Wagner.

This concert is broadcast on BBC Radio 3 tonight at 7.30pm. Act 3 is broadcast live tomorrow night at 7.30pm