OAE/Rattle/Malena Ernman, Barbican, London <!-- none onestar twostar threestar fourstar fivestar -->

Deputising as half of classical music's charmed couple has to be the one-night chance of a lifetime. When Magdalena Kozena sent in a sick note the day before her concert with Sir Simon Rattle, the window of opportunity opened for the Swedish mezzo Malena Ernman. She made her mark at Glyndebourne two seasons ago, the same year as Kozena. Most of the audience were initially busy being disappointed at the no-show, but it was clear that the Orchestra of the Age of Enlightenment had warmed to her, and by the end everybody knew why.

Tall and stately, Ernman turns out to possess a disarming smile and a voice that can apparently do anything and become anybody. Items from four Mozart roles, including one of each sex from The Marriage of Figaro, found her willing to try out all she could do.

First was Dorabella from Cosi fan tutte, given a dissection that would have sounded clinical were it not for the impact of the voice's wondrous sound. There was a trick with removing vibrato and a clucking staccato that sounded too calculating for a woman who, in the opera, is supposed to be on the receiving end.

Figaro's Susanna, who gives as good as she gets, took better to the treatment. She appeared in two versions, one in an aria written for a specific virtuoso singer and decked in florid runs and jumps. The other Susanna, in the more familiar "Deh vieni", showed that Ernman does languid as well as speedy. Her constant changes of colour sounded contrived, but arguably contrivance is what Susanna is up to anyway. After the interval, Ernman turned herself into Susanna's would-be lover Cherubino, and her singing became notably more fluent and relaxed.

To end, an aria from La Clemenza di Tito produced long, suave phrases over the agitated accompaniment, swooping down into a voluminous contralto, and a single non-operatic number - the showpiece "Laudamus te" from Mozart's C minor Mass - even managed a kind of echo duet between contralto and mezzo ranges among the bursts of energetic and joyous accuracy.

Rattle topped and tailed the concert with orchestral Mozart and Haydn. The Idomeneo ballet music was bold, bursting with counter-point and taut phrasing. A similar approach would have been just right for Haydn's Oxford Symphony, but the best things here were slow, from the questing introduction to an Adagio with the true Haydn feeling of a song of experience, catching the sense of loss.