Syesha picked "Vanishing" from Carey's self-titled 1990 debut album.
Carey thought Mercado was "cool, composed and did a great job."
It's another great performance, but I suspect she'll still be in the bottom three. Girl can't catch a break.
"That's probably the toughest song of the night," Jackson said. "You did a good job with it all things considered."
"Technically, it was very, very good indeed," Cowell said. "Having said that, at this stage in the game I'm not sure I would have chosen a song that not many people have heard of."