The panel were particularly pleased with single mum Crystal Bowersox, who performed Creedence Clearwater Revival's Long As I Can See The Light to rave reviews the day after she was hospitalised for an undisclosed malady.
"I feel good, I'm a tough cookie," the 24-year-old told host Ryan Seacrest.
Cowell admitted he "completely underestimated" Crystal after her performance last week. "I think we've got a serious artist with you," he said.
His fellow judges, Randy Jackson, Kara DioGuardi and Ellen DeGeneres were also impressed, with Kara saying Crystal "hit a new level tonight".
Other wannabes who won good reviews included 20-year-old singers Lilly Scott and Siobhan Magnus.
Other singers didn't fare so well, with Didi Benami, 23, almost brought to tears after the judges slammed her interpretation of Bill Withers' Lean On Me.
But Haeley Vaughn, 16, kept smiling as the panel ripped down her version of Miley Cyrus' The Climb. "You need about a year of strengthening your instrument," Kara advised her.
The top 10 boys performed the night before. The two male and two female semi-finalists with the fewest viewer votes will be sent home on Thursday, leaving 16 contestants to vie for a spot as one of the top 12 finalists.






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