CLASSICAL MUSIC / Sense and sensibility: Angela Hewitt - Wigmore Hall

Mendelssohn's unfashionable liking for Bach was not just scholarly pioneering, but acknowledgment of a vital creative source. The Mendelssohn Prelude and Fugue in E minor, Op 35 No 1, with which the Canadian pianist Angela Hewitt opened at the Wigmore Hall on Wednesday, is a brilliant idiomatic tribute and also a heady flight of fancy. Nothing could be closer to the language of Bach's 48 Preludes and Fugues than the loitering fugue subject and its firm andante exposition; yet by the end Mendelssohn, in a thrilling fast-forward, has glided into the enchanted caprices of his Midsummer Night's Dream music.

Angela Hewitt was the perfect exponent. A noted Bach player with chalky, clear, lively articulation, she is also bold and playful. The crazy accelerando and the fey catch-as-catch-can in the latter part of the fugue had the same imaginative confidence as the flaring spread chords that swept us into the legend theme of the prelude.

Quite right that a big personality like this should go on to measure itself against the Liszt B minor Sonata with its hectic virtuoso dashes between heaven and hell. Her slightly austere approach to pedalling meant that weird effects like the goblin rumblings at the beginning of the piece were realised with startling clarity. Even though she was at the edge of her physical strength in the heaviest passages, not getting the ultimate depth of sound, she never allowed technical challenges to undermine her dramatic command. Faced with a choice between losing impetus and fluffing an octave, she took the risk and fluffed the octave.

Not that this happened very often. Her technique was exceptional, even taking off at times into that rare daemonic hyperspace where anything seemed possible at any speed. She covered Liszt's whole emotional map from driven grotesque chromaticism to radiant chordal exaltation. Further refinements of colour, greater contrast between what was sharp and what was melting, would have supported the freedom of her approach and made her original and dramatic reading even better.

She did have one besetting sin: the 'sensitive' rallentando. Interrupted pulse suited her; or else a steady pulse enlivened with fugal surprises. On Wednesday she seemed unable to trust herself with simple continuous rhythms. Having stunned us with her mastery of a huge score like the Liszt, she didn't really make much sense of the tiny Satie Gymnopedie that she played as an encore, leaning and hesitating meaningfully over cadences that should have stayed artlessly in tempo. This was the crystallisation of a tendency that had, in the course of the evening, marred the start of the Mendelssohn, dissipated concentration in Liszt's idylls, and ruined the otherwise beautiful Maiden and the Nightingale of Granados: a masterpiece so short that any failure of nerve at the beginning leaves the central rhapsody hanging nowhere. She substituted compulsive rallentandi for perceptive tempo distinctions in the opening tangle of theme fragments: a surprising lapse into ordinariness by an artist who was mostly not ordinary. Samuel Barber's cool Sonata for Piano, written in 1949, made a springy sure-fire vehicle to finish the evening.