Sing it, LeAnn!

LeAnn Rimes  as been feeling under the weather -- but the talked-about country singer, 30, honored a commitment to croon on Wednesday night's X Factor with finalist Carly Rose Sonenclar.

Clad in a black leather dress and boots, Eddie Cibrian's wife appeared onstage with Sonenclar to sing her trademark 1997 smash, "How Do I Live."

Although Rimes occasionally seemed to miss the notes and flubbed a few lyrics, the twosome were met with thunderous applause -- and praise from judge (and another former kid and teen star) Britney Spears, who called the performance "shockingly amazing."

"That was one of the most fun moments I've had on the stage. It was amazing, I had a blast," Sonenclar gushed of Rimes. "You made me very comfortable."

"I love this girl so much," Rimes said of Sonenlar, 13. "She's such an amazing talent. I want to wrap her up and just hold her."

"I love my sweet and talented @CarlyRoseMusic on @TheXFactorUSA," Rimes tweeted right before the big show.

Performing on The Tonight Show with Jay Leno one night before, Rimes admitted she wasn't feeling her best. "I was and am SO sick," she said.