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Casey Abrams (season 10)
Casey Abrams' jazzy-bluesy style impressed the judges with performances such as ''I Don't Need No Doctor'' and ''Birdland.'' But it wasn't until Casey broke out his upright bass in Hollywood that the judges truly took notice of the former music-school student's deep musicality. His unique twist on Ray Charles' ''Georgia on My Mind'' left the judges dazzled.
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Haley Reinhart (season 10)
After nearly getting cut during the group round (''You made it by the skin of your teeth,'' warned Jennifer Lopez), Haley came roaring back with a hot, growly, and passionate solo performance of ''God Bless the Child'' that assured her a spot in the top 24. Jennifer summed it up simply as ''Redemption.''
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Andrew Garcia (season 9)
Before American Idol, Andrew Garcia's acoustic performances of pop hits had already made him a YouTube star. But would the judges appreciate his take on Paula Abdul's ''Straight Up''? With just his acoustic guitar in hand, Andrew's soulful, Latin-inspired flip on the pop classic turned out to be a risk worth taking. ''That was genius,'' gushed Kara DioGuardi, ''Paula would be screaming and yelling and clapping.'' Unfortunately, the performance set a bar Andrew was never able to meet again once he achieved a spot in the finals.
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Didi Benami (season 9)
In her initial audition in front of the judges, Didi Benami struggled through an emotional rendition of the Beatles ''Hey Jude'' — a performance she dedicated to a dear friend who had recently passed away. Nevertheless, this seemingly fragile singer-songwriter kept it together in front of the judges in Hollywood long enough to deliver a powerful and heartfelt rendition of ''Terrified,'' a song co-written by Judge Kara DioGuardi. No pressure! ''I thought that was terrific,'' said Simon. At that moment, Didi was the girl to beat, although she'd be eclipsed by eventual runner-up, Crystal Bowersox, once the finals began.
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Matt Giraud (season 8)
Simon Cowell was so impressed with Matt Giraud's initial audition performance of Gavin DeGraw's ''I Don't Want to Be'' that he compared him to another soul-inspired singer, season 5's third-place finisher, Elliott Yamin, who also covered the tune during the competition. But this former piano-bar player didn't become a contender until Hollywood, when he finally sat at the keys for the first time. His bluesy and confident take on Ray Charles' ''Georgia on My Mind'' brought the crowd to its feet. ''That was HOT!'' shouted Kara DioGuardi.
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Adam Lambert (season 8)
Simon Cowell dismissed Adam Lambert as ''theatrical,'' despite the fact that the glam singer hit some death-defying high notes during his ''Bohemian Rhapsody'' audition in San Diego. The ''just a theater boy'' image continued in Hollywood when Kara DioGuardi told Adam, ''I'm feeling like you're still doing musical theater,'' after his first performance. To prove he could interpret a song like a proper pop star, Adam took a risk with his next song, twisting Cher's disco classic ''Believe'' into a rock ballad. Not only did the singer finally impress Simon, but Adam made it clear that that there would be no hiding on the Idol stage.
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Syesha Mercado (season 7)
Syesha battled throat problems all week in Hollywood, even resorting to communicating with signs after going on vocal rest. It looked like Hell Week would do the songstress in, until the very last day of the round when she managed, still hoarse, to belt out a big, beautiful version of ''Chain of Fools.'' ''I think you are one to watch in this,'' said Randy after Syesha blew everyone away. ''You could sneak up and give everybody a run.''
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Chris Daughtry (season 5)
Simon rejected Chris Daughtry at his initial audition. But when the North Carolina rocker took the stage to sing Cat Stevens' ''The First Cut Is the Deepest'' in Hollywood, Simon began to change his mind and would eventually become Chris' greatest champion.
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Mario Vazquez (season 4)
Before Carrie Underwood became the darling of season 4, there was Mario Vazquez, who impressed the judges in Hollywood with an a capella rendition of the Queen classic ''Bohemian Rhapsody.'' He went on to impress in the semifinals with performances like ''Do I Do.'' Shortly after earning a place in the finals, Mario abruptly and mysteriously quit the competition.
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Frenchie (pictured, top)/Kim Locke (season 2)
It was the season 2 group rounds, but Frenchie and Kim sang as a duo because the other girls in Hollywood were ''apprehensive'' about singing with them. ''Frenchie has a big voice,'' said Kimberly, ''I have a big voice. It's not that they didn't want to sing the song... they just didn't want to sing the song with us.'' And no wonder. When these two ladies took the stage their huge voices on ''Band of Gold'' got the crowd's attention. ''That's the way to get everybody back from lunch,'' said Randy. Frenchie and Kim's impressive performances helped both earn a spot in the top 32 of that season. Unfortunately, Frenchie was disqualified after risqué photos of the singer turned up online.