NEW YORK — After it was announced that Fantasia would take over the lead role in the Broadway musical "The Color Purple," she recalls her co-stars as being warm, friendly and supportive. Still, she knew in the back of their minds that they had doubt about her casting.

Perhaps for good reason. The former "American Idol" champ was taking over for LaChanze, who won a Tony for her portrayal of the downtrodden Celie, and the 23-year-old's acting experience had been limited to a saccharine Lifetime TV biopic in which she played herself — not exactly the most challenging of roles.

And then there was the whole celebrity factor that's permeated Broadway in recent years — putting stars such as Usher, Brooke Shields, Deborah Gibson and other assorted A- to D-listers in stagnant productions to boost box office.

"A lot of times they give us hard times, and they say, 'They're bringing in such and such on Broadway just to bring in money, because they probably ain't gonna do so good because they haven't been acting all their life,' " Fantasia says.

That made her even more determined.

"I was like, 'I have to go in here and do my best for them. It's not only me, but it's a whole cast who's been doing it for two years, and I have to hold the show up so that we will have a good show,' " she says.

Since her arrival in April, she has done more than hold up the show. She's revitalized it. Fantasia has received rave reviews, boosted a box office that had started to slump and, some say, improved a successful commercial production that was lacking critically. The New York Times called her "so terrific that this earnest but mechanical musical is more effective and affecting than it was when it yawned open a year and a half ago at the Broadway Theater."

"I think she's clearly given the show a new burst of energy that everyone is enjoying the benefit of," says Scott Sanders, one of the show's producers.

"When you bring in someone who is a household name, it brings out the cynics who think that it is just stunt casting and those who actually understand that she is a very talented woman who is going to take a big leap. ... It's turned out to be an incredible win for everyone."

But it hasn't come without sacrifice. A few hours before show time, the doe-eyed singer, clad in sweats with her hair closely cropped, lounges in her midtown apartment, looking weary — far from her usual animated, gregarious self. As she walks around gingerly, she blurts out: "This show is kicking my butt!"

Part of what makes her so tired is the grueling schedule. She performs eight times a week and is onstage almost the entire production, singing with such a fiery passion that you get exhausted just watching her. After curtain calls and on her days off, she sleeps, sleeps and sleeps:

"I ain't never heard the sleep word so much in my life until I got on Broadway," she says with a laugh. "I'm so tired — mentally tired, physically tired."

The content of the show has also drained her.

"Miss Celie takes a lot of out of me," Fantasia says in her soft, raspy Southern drawl, in between bites of a light lunch. "I'm being told every day that I'm ugly. ... you can't play the part if you don't kind of put yourself in her shoes and live her life. So it's like, I carry that stuff with me."

It's easy to see why Fantasia can't shake some of Celie's blues. In many ways, she shares parallels to the famously put-upon character who originated in Alice Walker's acclaimed book. Like Celie, Fantasia has lacked in education (she quit in high school), had a baby in her teens and suffered sexual abuse (Fantasia says she was raped by a classmate).

"I put myself in her shoes in having (daughter) Zion at such a young age and dropping out of school and being in just bad relationships and disrespected," she says.

Still, even though she could identify with Celie, Fantasia wondered if she was the right person to take on the emotionally complex character, who goes through several decades and transformations by show's end.

"What makes them think that I can do that?" she recalls asking herself once she saw the show.

For Sanders and Oprah Winfrey, the show's most prominent producer, it wasn't that hard to imagine.

Says Sanders: "I had a hunch that because of her rawness in her ability to catch material and deliver it, in such a profound and powerful way, if she could get inside the character of Celie, or let Celie get inside of her, that this could be a really unique opportunity for everyone."

Fantasia has done so well that the show's producers have talked her into extending her engagement by four months, until January. But she hesitated before signing: Not only was she drained, but she worried about taking more time away from her recording career.

It wasn't until she had a chat with Winfrey (she calls her "Miss Oprah") that she began to warm to the idea of playing Celie a bit longer. "She just began to tell me how much I touched her and all the things that she felt," Fantasia recalls. For Fantasia, that did it.