Melanie Amaro was worried about stepping out of her R&B comfort zone to tackle the Eagles' classic rock hit 'Desperado' on the 'X Factor' tonight.

Amaro was brought back on the show by Simon Cowell after being rejected in an earlier round. Cowell admitted he made one of the biggest mistakes of his life when he let Amaro go.

With her performance of 'Desperado,' Amaro not only proved that she belonged on the show but set herself up as a frontrunner on 'X Factor.' She delivered a pitch-perfect version of the song, wowing the judges and the audience.

"There is no limit to what you and your voice can do," said judge Nicole Scherzinger, while Paula Abdul said her voice was like "fine china."

Her mentor Cowell told her, "I didn't realize how good you werer ... Right now you are the one to beat, trust me!"

Watch Melanie Amaro Perform 'Desperado' on the 'X Factor'