This weekend's episodes of the BBC talent show have seen the foursome whittle down their teams to just three artists each ahead of the live shows.
But the 'Price Tag' singer got more than she bargained for when she pit Danny County, Sarah Cassidy and Trevor Francis against each other for one of her three spots.
Each of the hopefuls had to belt out a 'killer song' that they thought would convince Jessie to choose them.
Danny picked The Ronettes' 'Be My Baby', Sarah went for 'Ain't No Mountain High Enough', and Trevor settled on 'Gimme Some Lovin' after seeking help from his wife.
Following their performances, Jessie commented: "I am so proud. I don't even know. I don't know. Seriously, I need some guidance."
"The one that came across the stronger and had the most power, for me, was Trevor," said Tom Jones.
"The difference between Trevor and Sarah is so slim that Sarah's song choice tipped it for me," reviewed Danny O'Donoghue. "She knows how to get a crowd going."
Will.i.am was more blunt with his critique, commenting: "Danny, you're my favourite, but that wasn't good. The only percussion I heard was my head hitting the chair when I fell asleep.
"Sorry, I'm being honest, but I would still pick Danny as I don't think he was given the right tools."
Still unable to come to a conclusion, the panel gathered around Jessie's chair to offer some more advice.
Eventually she concluded: "Danny I'm being real with you, I believe you are the most unique artist this show has ever seen, but I'm not gonna put you through because I don't think that was the best voice.
"I'm gonna go with the person that showed me something that I haven't seen that deserves to fight in the lives, so the winner of this knockout is Sarah."
Jessie later claimed that the decision was "the hardest thing I've ever had to do".
The first of The Voice UK's live shows airs this Friday at 7.00pm on BBC One.