The singer explained in a video package before this week's performance that she had chosen to keep her Virgin Islands accent hidden because she had been teased about it as a child.
"When I first came to America my accent was so very, very strong that people would make fun of me. I had to learn to cover it," she said.
Amaro added: "I felt like I was an outcast, like everybody pushed me to the side like, 'I can't understand the way she speaks'. Once I started to speak in my normal accent I feel like a burden was lifted.
"It just came out, it just happened."
Her mentor Simon Cowell added: "I was actually really happy for Melanie. She has the freedom now to be what she is, which is an amazing, amazing singer."
Amaro performed the Michael Jackson classic 'Earth Song' at the end of Wednesday night's King of Pop-themed performance show, which was watched by the late singer's family members including children Paris, Prince and Blanket.
Cowell told her that he "could not be more proud" of her and that it was a fitting tribute to Jackson.
LA Reid added: "For one second I forgot we were in a competition and I felt we were at a Melanie Amaro concert. You were amazing and maybe the best of the night." Nicole Scherzinger agreed, but went on to say: "It was one of the best performances I have seen on this entire show."
Paula Abdul was equally enthusiastic in her praise, telling Amaro she was "flawless" and had "nailed" the song.
The other acts in the running for the $5 million prize are: Astro, Marcus Canty, Chris Rene, Drew, Rachel Crow and Josh Krajcik.
Two more acts will be sent home in another double elimination tonight (Thursday, December 1) at 8/7c on Fox
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Watch Melanie Amaro's performance below: