Alex and Sierra, the resident lovebirds on this season's X Factor, took on Destiny's Child's "Say My Name" on Wednesday night in front of the singing competition's judge Kelly Rowland, who is one of the song's original singers.
The soulful performance, which starts at 2:30 in the above video, impressed Rowland.
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"I must admit I was not ready for that ... I was really shocked, but you guys really, actually pulled that off," Rowland told the duo during the judges' critiques.
Destiny's Child released "Say My Name" as a single in 2000, and it went on to win two Grammys for Best R&B Performance by a Duo or Group as well as Best R&B Song.
The pair also performed "Say Something" by A Great Big World and Christina Aguilera:

Wednesday's show on Fox featured the top six acts remaining in the competition. One act will go home on Thursday, leaving five to vie for the X Factor crown.
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However briefly.
The boy band tried to deny it, but superfans' reunion senses were tingling.
Complete with a kiss between Uncle Jesse and Aunt Becky.
With it, came the subsequent rush of Boy Meets World lists.
Hopefully with absolutely no change to the classic '90s cover art.
Yes, she came back briefly before, but we're not going to talk about it.
Soon you'll be able to secretly feed your beloved digital pet 'digital pet during meetings instead of math class.
It's been 14 years since the original, but better late than never.
And all the real life Britney karaoke sessions it undoubtedly inspired.
From the scrunchies to the Trapper Keeper.
In heaven, Backstreet is always back.
Image: The X Factor