It would be the most unlikely of circumstances if the 2004 race for "American Idol" was essentially won thanks to a 70-year-old Gershwin classic. Throughout the highly vocal "Idol"-verse, they're still talking about Fantasia Barrino's performance of "Summertime," in which she took the stage with her feet and emotions stripped bare.

"When I got up from singing the song, I was crying, because it touched me," Fantasia recalls. "And I was saying 'Hopefully if it touched me, I hope it touches someone else.' Obviously, it did touch somebody else."

Fantasia's raw and passionate interpretation of the song, which has to be considered one of the season's very best performances, is the 19-year-old singer's defining moment in the competition. It almost never happened.

"I'd never heard that song before in my life," she admits.

The show's musical director played the song for Fantasia and got her interest, but she only became hooked when she realized that "Summertime" is a lullaby, sung by Clara to her baby. The North Carolina singer saw the chance to perform a song to her young daughter Zion.

"She's a joy," says Fantasia. "She's a blessing that God gave to me and Mommy's gonna work so that she can have the best... I get tired, I get weary, but sometimes I think, 'I have a child to take care of, so I've gotta work hard.' She pushes me."

Considered a favorite since the audition rounds, Fantasia has matured as the competition has progressed. In the earliest weeks of the show, she won fans for her spunky willingness to stand up for herself and talk back to the judges, but that candor also proved a negative. Some viewers (obviously a minority) interpreted her confidence as a bad attitude and the signs of defiance have decreased with each passing week.

"It wasn't that I was trying to be smart and mean and attitude," Fantasia insists. "It's just how I am with them off-stage. Off-stage if he says something to me in the back, I'm like 'Simon, oh be quiet.' He's got a lot of mouth so I always just get him back.

"I just wanted to show people that that wasn't me," she says. "When I heard about it [negative comments], I was like 'Aww man, I don't want people to take me that way, because I'm not that way.' So I just shut up."

Fantasia's temperance has been aided and abetted by comments from the judges that have generally run the limited gamut from gushing to raves. Now, though, she has to go one-on-one with Diana DeGarmo, a 16-year-old who Fantasia compares to a little sister.

"If she wins it, I'm gonna be so happy for her," she says. "I'll probably be crying like I always do every Wednesday -- big crybaby. If she wins it, if I win it... I'm pretty sure it doesn't even matter to her."

Given that industry legend Clive Davis pretty much guaranteed her a recording deal when he served as guest judge last week, Fantasia knows that she's going to get her chance regardless of how this week's voting goes.

"To me, right now, it really doesn't matter, but I'm not going to do anything different," she says. "I'm gonna still get out there and sing like I've never sung before."

Fantasia Barrino and Diana DeGarmo sing like they've never sung before on Tuesday night at 8 p.m. ET on FOX. The two-hour finale airs on Wednesday night, beginning at 8 p.m.