LSO/Sir Colin Davis, Barbican, London

Two different worlds, Sibelius's Sixth Symphony and Brahms's First Piano Concerto, separated by an interval – they made an unusually satisfying, clear-cut programme at the weekend. The works have one thing in common, for they're both in D minor, though that hardly describes the modal, "white-note" feeling of the symphony, shot with chromatic dissonances like exquisite stabs of pain. The serenely drifting opening is one of the most beautiful beginnings in the symphonic repertoire; it's what everyone mentions, forgetting the rest, which is disturbing, unexpected, and, possibly, inconclusive, though none the worse for that. Sibelius went on quickly to write the much more decisive, straight-line Seventh Symphony afterwards. Admired by connoisseurs, the Sixth is not yet as popular as it deserves.

I feared (could this be prejudice?) that Sir Colin Davis might find a way to wallow, or over-dramatise. He didn't, and his gestures were gentle, his beat more economically defined than usual. Given well-judged tempos (and they were), it was up to the orchestra to play to their highest standard (and they did): the London Symphony Orchestra's strings, all important in this work, are certainly not bettered in London. The recording they were making on Saturday, and at the repeat concert on Sunday, should be pretty well immaculate.

Despite the double opportunity, it seems amazing that the hall wasn't packed for Radu Lupu, whose Brahms is second to none. This was the quietest performance of the D minor Concerto I have heard, but it certainly had gravitas. For once, there was no feeling of awkwardness about tempo when the soloist entered, for Lupu floated lightly over the easy swaying motion murmuring in the background. Paradoxically, by ignoring the bait of Brahms's "espressivo", he made an expressive point. This was real concerto, or "concertante", playing, and briefly, during the slow movement, Lupu half-turned his back to the audience the better to see the woodwind players and merge his accompanimental arpeggios with their more important parts. A few seconds earlier, challenged by Lupu's delicacy, Davis hushed the strings to such a level that I thought the music might have stopped. That sort of breathtaking moment only occurs in a live performance – it would be artificially boosted in a recording.

Yet the concerto's assertive qualities were done full justice, too, and the powerful passages were impressive without being hectoring; the famous double trills in the first movement sounded like a musical sonority rather than a display of unlikely strength. If you had thought Brahms was unduly overbearing, you might have changed your mind after this.