Britney Spears on the X Factor Season finale on December 19, 2012. Credit:

Britney Spears has been a fashion tour de force during her inaugural season as a judge on The X Factor.

Night after night, the pop superstar wowed in form-fitting frocks, midriff-baring tops, and sexy minidresses that showed off her lean legs. But on the Wednesday, Dec. 19, show -- part one of the competition's two-part season finale -- the 31-year-old mentor kept her look modest and let her star contestant, Carly Rose Sonenclar, have the spotlight instead. Sporting a black Yves Saint Laurent jumpsuit, black-and-white heels, and a long Erickson Beamon beaded necklace, Spears was the picture of understated chic.

Sonenclar, on the other hand, looked -- and sang -- like a true star-in-the-making. Facing off against Fifth Harmony and Tate Stevens for a $5 million recording contract, Spears' 13-year-old protege performed pitch-perfect renditions of Nina Simone's "Feeling Good," Leonard Cohen's "Hallelujah," and LeAnn Rimes' "How Do I Live" -- with Rimes herself!

"I just feel like it's shocking how bright your star is, and we're going to win this," Spears told her contestant.

Later, after Sonenclar's cover of "Hallelujah," she added: "That performance alone is worth five million bucks, so you should get out your checkbook, Simon [Cowell]."

The X Factor finale aires Thursday, Dec. 20, at 8 p.m. EST on FOX.