Britney Spears needs to work on her poker face. 

Simon Cowell's girl group, Fifth Harmony, was the first act to advance to next week's X Factor finale -- and the 31-year-old pop princess was none to pleased about it. Gritting her teeth, Spears pursed her lips and widened her eyes in disbelief, though she made no attempt to console her lone remaining act, 13-year-old Carly Rose Sonenclar.

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With her own contestant's fate still in jeopardy, Spears looked increasingly uncomfortable during the one-hour Dec. 13 episode. "I was a little disappointed," she said when asked to explain her funny faces. "I thought it was going to be the other way around with the groups."

In a twist of fate, Cowell's other group, Emblem3, was eliminated. Sonenclar, Tate Stevens and Fifth Harmony will vie for the $5 million prize Wednesday, Dec. 19, with the winner being revealed the following night.

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Despite her moody facial expressions, Spears looked sensational in a sheer paneled mini-dress by Alexandre Vauthier and Yves Saint Laurent heels. She later downplayed her nerves in a Facebook post. "Congratulations, Carly Rose!" she wrote. "I wasn't worried for a second -- to the finals we go! So happy to be a part of this journey with you sweetie. Wow!"

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The "Scream and Shout" singer added, "To my Britney Army and everyone that voted for Carly last night -- this is a big moment for us all to be proud of. Thank y'all so so much!"

This article originally appeared on Britney Spears Wows in Sexy Dress, Makes Funny Faces on The X Factor