It's the battles and Katie is pitched against Sarah Cassidy by mentor Jessie and her battle advisor Claude Kelly.
Jessie chooses Katy Perry's ET for the pair to duet on, but Katie admits her concerns in training to the cameras.
The youngster says: "I feel like all my influences have been forgotten in this song. When I hear Sarah sing it I feel it suits her voice."
As the performance approaches, a nervous Katie is seen crying, and admits she's worried about her much older competition: "She's [Sarah] had a lot of training and experience, which I haven't had."
But it's only after the battle itself that Katie opens up about her concerns over the song choice, revealing to the other coaches and host Reggie Yates: "With no disrespect to Jessie J, that song didn't get to show the real me and what I'm capable of."
Jessie J remarks to the cameras: "I'm upset she didn't tell me she didn't like the song."
She adds: "The song for me was so simple, it was one note that she could put herself on."
Tomorrow night's first battle round also sees some real rivalry between Cleo Higgins and duo Nu-tama, who go head to head on Team Will.
After a very noisy performance from the three girls, Jessie J tells them: "I feel like I've got a headache, it was all too much."
The Voice UK airs Saturday at 8:35PM on BBC One.
Browse pictures of the first Voice 2013 battles below...