Amaro, Chris Rene and Josh Krajcik performed for America's votes for the final time on Wednesday's edition of The X Factor, which also featured the Top 3 paired with R Kelly, Avril Lavigne, and Alanis Morissette for duets.
Thursday's final will see one of the three competitors win The X Factor's $5m grand prize.
Ryniewicz will take part in tonight's show as well, when she sings with her idol Justin Bieber.
When quizzed by the show's official website about her thoughts for the final, Ryniewicz insisted that she is solidly supporting Amaro.
"This show has got crazy talent, but once part of Team Simon [Cowell], always part of Team Simon," the Chino Valley, CA native said.
Ryniewicz added: "I'm still rooting for Simon and his girl! So go Melanie! Melanie has got this huge range and not everybody can sing like that."
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The recently eliminated Marcus Canty has admitted that he's torn between supporting Rene and Krajcik, while the other finalists have split their votes between the Top 3.
Tonight's X Factor finale will not only crown its first champion, but will also feature performances from Stevie Wonder, Pitbull, Leona Lewis and 50 Cent.
The X Factor airs tonight at 8/7c on Fox.
> X Factor USA final part one pictures: Avril, R Kelly, Alanis
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Watch Melanie Amaro perform 'Listen' below: