London Philharmonic/ Belohlavek, Royal Festival Hall, London

Midway through the London Philharmonic's current Mahler festival, the Czech conductor Jiri Belohlavek persuaded the orchestra to treat the Symphony No 5 to one of the most idiomatic performances this much-played composer has had all year. This was in a different league from the record market's favourite, Simon Rattle, conducting the same symphony, or Mariss Jansons's hard-driven No 6 in London last month, both with technically superior orchestras. It was quite a concert, especially since something even better had happened in the first half.

Richard Goode being indisposed, Stephen Kovacevich took over as pianist, changed the Mozart concerto to No 24, and delivered playing special enough to beat the disappointment of missing Goode. A restrained orchestral opening was transfigured by Kovacevich's first phrase, which prolonged the first main note almost beyond belief yet kept perfectly in tempo. He was to match this rhythmic feat of subtlety and quiet expressive force again and again. Just as affecting was the minute variability of his phrasing, which contributed nuances of energy and emotion without fuss, and a sly stroke of wit in the switch to a quick pace at the end. Apparently limitless rhythmic freedom and dynamic range took place within strict classical confines. Perhaps nobody else can play the piano with this degree of precision and turn it to such musically intense ends.

Belohlavek, like Kovacevich, is proving an artist who has become more inspiring in their middle years. The Mahler symphony immediately found the key to its composer's heart, by way of understanding how to make the rhythmic detail flexible enough, and the piled-up melodic lines shapely enough, to reinforce the sense of a larger whole instead of fighting against it. The fast opening movement conjured a raging grief spiked by Mahler's authentic angst.

The big revelation comes when its most sorrowful phrase, played over and over, suddenly shows itself by a switch of harmony to be the source of its most triumphant one. This was rightly made the pivotal climax, prepared for many minutes and always picked up in the references that follow through the rest of the work. After it, the later stages became easy-going at times, but always prone to turn sinister with a deft stroke of orchestral colour, full of character without needing to lay on the gloss.

The Adagietto was expansive and simply phrased, a love song rather than a loading of life's frustrations on to a structure that can't take it. Some outstanding quiet playing at speed led the finale through successive tautenings of pace with the flexibility to relax and then take the tension up another notch.