"I'll tell you who I like, I like this girl Crystal," said Cowell during a Monday night appearance on The Tonight Show with Jay Leno.
"I have to admit, when I first saw her I described her as a busker and I like the way she handled that because she kind of admitted that's what she was. She's got some confidence now. She was ill, she got over that. She's got a great voice. She's different."
However she subsequently wowed the judges with her rendition of Creedence Clearwater Revival's "Long As I Can See The Light" during Wednesday night's performance episode.
"I promise you, this was like the moment we realized with Kelly Clarkson that we've got a serious artist here," Cowell told Bowersox following her performance. "I think we've got a really serious artist with you, congratulations."
"I think sometimes it becomes a popularity competition," answered Cowell. "That's what I think happened last year. I like the winner, but I personally thought Lambert should have won as an overall artist."
In addition, Cowell continued to play coy about the possibility of former American Idol judge Paula Abdul serving as a judge on his The X Factor reality series when it launches stateside on Fox in Fall 2011.
"I don't know yet, but I will definitely be doing something with her," he said.