Mahler's first symphony was an astoundingly precocious work for a man of 24, and Valery Gergiev, in this latest stage of his Mahler cycle with the London Symphony Orchestra, seemed determined to test its originality to the limits. Yet the conductor did not reveal his intentions immediately. The symphony's supremely atmospheric awakening was taken almost conventionally, with Gergiev seemingly content just to dwell on a skittish phrase here or touch in a colouristic detail there.

Once the darker side of Mahler's imagination made its appearance, however, Gergiev took the symphony by the scruff of the neck. The first movement ended in a massive broadening of tempo, followed by a manic acceleration in the final bars. The earthy second movement was high-octane, full-toned and cocksure. No Wunderhorn charm or lilt for Gergiev here; rather, a Tchaikovsky-like defiance of fate.

The funeral march was an exercise in barely suppressed hysteria, brilliantly illuminated by the LSO woodwinds. Most conductors permit a sense of fulfilment and spatial grandeur as the close approaches. Gergiev was unremitting; aggression and dissonance held the stage to the very end. If you like your Mahler visceral, spine-tingling and dangerous, this was for you.

The LSO are certainly playing out of their skins for Gergiev these days. If that was dazzlingly obvious in the Mahler symphony, it was more subtly illustrated in Schoenberg's 1903 symphonic poem Pelleas und Melisande, which preceded it. This score can sound aimlessly dark and meandering. But Gergiev found a clear sense of direction within the work's dense textures, and the snarling brass, bubbling woodwind and velvet stings of the LSO gave it a feeling of implacable momentum, which it can sometimes lack in less committed hands.

· Radio 3 broadcasts Gergiev's Mahler cycle beginning January 28.