Kelly Clarkson prepares to rock Auckland

Kelly Clarkson can always pick out the adults who come to her concerts just to chaperone their kids.

At the beginning of the show they have a look of resignation, fully prepared to endure two hours of teen-pop drivel. But by the end, she says, their expressions have changed.

"It's like shock on their face. Because they're like, 'I cannot believe I enjoyed your concert'," says Clarkson, 23.

She has been getting that sentiment a lot these days. The cheese factor that surrounded her inaugural American Idol win and subsequent album debut, Thankful, has melted away. What has emerged is a credible singer-songwriter who is having critical and commercial success with an album full of undeniably catchy rock grooves such as Since U Been Gone and her latest, Behind These Hazel Eyes.

"This one is setting me apart just a bit more," she says of her latest album, Breakaway, which has sold more than 2.6 million copies since its release.

"I have a huge voice, so it's a bit more like a Janis Joplin vibe than a younger rock vibe. And I think that's what throws people because they don't know how to take me. Even critics - they don't know how to swallow me because they're like, 'Well, she came up like a total pop act'," says Clarkson, in her husky voice, more raspy than normal after an early morning TV performance.

"It's very different and I think that's what confuses people and throws people off, but at the same time I like that, because then it keeps you wondering what I'm going to do next."

Few would have predicted the wide reach of Since U Been Gone, the heartbreak anthem that peaked at No 2 on the Billboard Hot 100 chart earlier this year.

Not only was it a smash, but it attracted admiration from unlikely hard-rock fans and critics, and was a favourite mash-up candidate on the internet (one of the best mixes of Clarkson's vocals was with the music from The Eagles' One Of These Nights). But if fans had heard the original version of Since U Been Gone, produced by Max Martin, best known for crafting the hits of the Backstreet Boys, Britney Spears and other teen-pop artists, they might not have been very impressed. Clarkson says it was "very contrived, very pop".

"I was like, you know, it's a catchy song, I could sing the heck out of it, but I don't think this is my vibe," she says.

But instead of rejecting the song outright, she suggested reworking the song to give it a rock edge.

"What's funny is [Martin] didn't like it [either] ... we had the same exact idea," she says.

Clarkson has taken a more hands-on role in her career since winning American Idol three years ago. She's changed people behind the scenes, most notably ditching Simon Fuller, the American Idol creator, as her manager and switching to the powerhouse company The Firm.

"He's a great guy, sweetest guy, really wants dreams to come true for people," she says, attributing the split to Fuller's demanding schedule. "If he could have been with me every day ... I would have stayed with him in a heartbeat, and he knows that."

Clarkson hasn't kept up with the programme itself. She didn't make an appearance on this year's show, and didn't watch the competition because of her touring schedule.

But she knows she'll always be identified as an American Idol - and she's fine with it.

"I don't really mind; that's where I got my start," she says. "They always talk about the big first thing that you did. I think the only thing that I do mind is I don't want people to only focus on that."

Who: Kelly Clarkson, American Idol
Where & when: Logan Campbell Centre, Auckland, Tuesday November 22
Also: The final of the second series of NZ Idol screens tonight, TV2, 7.30pm