Their mentor Will.i.am pitched the two teenagers against one another on a cover of Alanis Morissette's Ironic.
"I paired Frances and Kate because they reminded me of me when I started dreaming, both of those girls would've been down with the Peas," Will said.
However the two girls weren't keen to go head to head, with Kate saying: "We're going to think of it as more of a duet rather than a battle. We're going to help each other pull through it."
But Will warned: "This ain't the get along gang, it's mortal combat."
On stage and the pair performed a beautiful take on the original track, leaving Will with a tough decision.
The Black Eyed Peas frontman reasoned: "Frances – you’re amazing.
"Kate – the way you sing is the type of singers I like. It’s like Sade’s, Macy Gray’s, I like Morcheba, Sneaker Pimps, that’s the kind of stuff listen to.
"Frances sounds nothing like Kate, Kate sounds nothing like Frances."
Giving his final decision, Will added: "But Frances is a chameleon. She could sound like whoever’s next to her. That’s what you’re getting. This is hard - very, very hard, because it feels like letting go of friends. So the person I want to take with me to the live rounds... I want to take Frances with me on to the live rounds."
Watch [tag]Frances Wood[/tag] and [tag]Kate Read[/tag] below...