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Carrie Underwood told Ryan Seacrest why she limped off stage after performing on American Idol Tuesday night.

"You're gonna laugh at me, everyone does," the Season 4 winner jokes on Seacrest's KIIS-FM radio show.

"I was running last Saturday in my little community [in Nashville]...It's about three miles," Underwood says. "I was about halfway through and I fell."

"And this nice lady was driving behind me -- I'd never met her before," Underwood continues. "She saw the incident and was nice enough to pull over and roll down the window and say, 'Can I take you home?'"

"So I fought back tears and she took me home!" Underwood says.

The country singer says her injury "looks ugly" but isn't too serious -- and it's the reason she donned denim and high boots for her performance.

"I haven't worn jeans. I pick sundresses and shorts, so I wore jeans and that hurt!" she says, joking that it also affected her choreography.

Underwood also remembers being in Kris Allen and Adam Lambert shoes a few years back.

"You feel the emotion, so nervous," she says. "But they're so proud. They did themselves great. I just wanted to cry each time either one of them did anything. Just a good moment."

As for who will win, "I think it's up in the air," Underwood says. "I think there definitely seems to be a lot more outspoken people for one person in particular -- but you might be surprised."

Underwood says she "blacked out!" after her win, but now she feels like "old Idol.

"It's so weird that this is, like, my job," she says. "I was just thinking about coming to Idol and doing my thing...and I thought, 'Holy crap! I'm famous! Oh my god, how did this happen?' It's the biggest show of my generation and it's just an amazing thought."

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