The country trio, who scooped five trophies at last weekend's Academy of Country Music Awards, recently taped a rendition of 'Need You Now' for the Fox competition, which will air on tonight's results show.
Speaking to MTV News, frontwoman Hillary Scott said: "It was amazing [after] watching it on television so many times.
"Then you get in there, and the room is not as big as you think it's going to be, but it's just as beautiful. We had a live audience, and it was fun. We were just honoured to be there."
Scott went on to joke: "I tried out for the show twice and didn't make it past the first round. So that is what you call validation!"
American Idol airs tonight at 9/8c on Fox.
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