First Night: The Misanthrope, Comedy Theatre, London

There are many reasons for deploring the money-mad practice, beloved of certain producers, of promoting wholly inexperienced film stars to abrupt centre-stage status in order to make a fast, dishonest buck in the West End. One of the chief of these is that it can warp the very meaning of the play into which the newcomer is parachuted. Remember Up For Grabs? Given its English premiere in 2002, this was supposed to be a satire about the inflationary commercialism of the art market. But how could it continue to hold its head up high when the leading role was assigned to Madonna and when the Material Girl's presence led to the precisely the phenomenon that was being lambasted onstage, with tickets exchanging hands for a ludicrous £500 a throw.

You might have thought the same would be the case, with knobs on, in Thea Sharrock's excellent, platinum-cast revival of this 1996 contemporary update by Martin Crimp of Molière's great satire against both the amoral courtly rumour-mill and an extremist hatred of courtly malpractice.

Played by a brilliantly tetchy and (to just the right degree) faintly ridiculous Damian Lewis (think fashionable Etonian hunk rendered all the more dogmatic by a tiny worm of self-doubt), the misanthropic Alceste is transformed into a terminally disgruntled playwright in Crimp's adaptation. The world he hates is the sycophantic, nepotistic, nihilistic media village of sloppy, relativistic postmodernism. So if there's a practice he'd be almost bound to abhor it is that of casting film stars in plays such as his, and he'd dislike it all the more because the major flaw in his armour is that he has allowed himself to fall for a soulless sliver of bitchy Hollywood starlet called Jennifer.

Though the decision has certainly had the cash registers ringing their rocks off, the production was therefore in danger of breaking the play's own implied moral code by casting Keira Knightley, here treading the boards for the first time, in this latter role. The critical knives were unsheathed and quivering. So it's a tonic to report that Knightley finesses all this ethical fussing by turning in a performance that is not only strikingly convincing but, at times, rather thrilling in its satiric aplomb.

A poster-girl for natural thinness, she makes Olive Oyl look chunkier than Roseanne Barr. It's not just that she cuts a stunningly beautiful figure here; it's that she has real stage presence and knows how to use it.

Show this character a back and she will feel compelled to ruin a reputation behind it and, as a kind of more chilling variant of Alceste, she is first seen playing the virtuosic, I-diss-therefore-I-am cow to her toadying entourage. Knightley captures the driven irresponsibility of these friend-nuking flights with bravura brazenness.

She is also extremely fine in the scene where she turns the tables on her Lee Strasberg-like acting guru, Marcia, a parasitic vulture masquerading as a martyr-to-her-client. This female is brilliantly nailed by Tara Fitzgerald, who is clearly enjoying playing a resentful frump against her normal glamour-puss type.

And in the hallucinatory Molière-period costume orgy at the end, Knightley rises from the ashes of her wrecked name not so much like a phoenix as like an incorrigibly shameless languorous lizard who can suborn anyone with her manipulative sexiness. She extends a beautiful arm to one haplessly smitten victim in a gesture that is like de-creation's answer to the outstretched arm of God to Adam in Michelangelo.

In a uniformly excellent cast, Tim Mullen is hilariously funny as a theatre critic who is trying to promote the script of his abject play. This figure's throwback idea of trendiness (jeans and double-breasted blazer) and his woefully misguided celebrity-seeking-missile manner suggest that Mullen has been doing inspired research in a certain neck of the Sunday market.