POP MUSIC REVIEWS : Stevie Nicks, Twirling Through the Past, Falls Flat : The singer, who will perform tonight at Irvine Meadows, relies on 20-year-old hits and mannerisms. But the crowd doesn’t mind.

LOS ANGELES â€”  Can you believe it’s been nearly 20 years since Stevie Nicks joined Fleetwood Mac and helped turn the fading blues-rock band into a pop powerhouse?

Apparently plenty of people can’t--or won’t--accept that passage of time. At the Greek Theatre on Thursday, for the first of two Nicks shows there, a full house of fans clung to every word and note she sang as if hers was the voice of an oracular priestess. But no one seemed in deeper denial than the star herself, who continues to play a role that was charming (if fey) when she was a lithe young woman in her 20s but should be rather embarrassing for someone approaching middle age.

Nicks--who will be at Irvine Meadows tonight--is still dramatically running off stage to change shawls every other song or so (six different outfits on Thursday). She’s still twirling (albeit more slowly these days) to accent the unicorns-and-rainbows-ish imagery she often favors. And still relying on songs from the first two albums she made with the Mac as the foundation of her show (because, let’s face it, her more recent material doesn’t measure up).

And when she did the old songs--�Dreams,� “Rhiannon� and “Gold Dust Woman,� accounting for a quarter of Thursday’s set list--she and her band made them virtual carbon copies of the mid-tempo Mac originals, save for Nicks’ now-limited vocal range.

Ironically, the highlight of the show was, in fact, a blast from the past but a borrowed one: an encore of Tom Petty’s “I Need to Know,� done with an energetic, no-frills approach that finally blew her out of her time warp.

* Stevie Nicks sings tonight at Irvine Meadows Amphitheatre, 8800 Irvine Center Drive, Irvine. 8 p.m. $26 to $47.50. (714) 855-4515.