It was one of the hardest decisions that Christina Aguilera had to make on "The Voice." 

The pop-singing diva chose underdog Lily Allise as the last member of her team to advance to The Live Show rounds next week.

"We are getting down to the nitty gritty," said Aguilera. "There is so much detail that goes on into this."

The battle rounds concluded as Aguilera paired up two polar opposites to duel it out – Allise, the soul singer, and Cherie Oakley, the only country music singer on Aguilera's team.

Singing American Idol alum Kelly Clarkson's "Since U Been Gone," the two contenders had to show Aguilera they had what it takes to sing pop hits. 

"The song has a lot of vocal range," Aguilera said. "You have to have some lungs in your little body."

This certainly put pressure on the odd pair.

"I definitely feel a lot of competition," Oakley said as she watched Allise show off her vocal ability during rehearsals.

Nevertheless, Aguilera made clear what she wanted vocally from the contestants.

"I'm not looking for perfection," she said. "I'm looking for passion and emotion."

"It's going to be really hard for me to send one of my babies home," she added somberly.

During the performance, the coaches were stunned with Oakley's control and confidence, and with Allise's attitude and stage presence.

"Christina took a second chance on me, so I'm not going to let her down," Allise reinforced.

And she most certainly did not. Aguilera couldn't resist, and sent Oakley home packing.

"It's so hard. My two angels," Aguilera said hesitantly. "My decision is...Lily."

Allise now joins Javier Colón, Vicci Martínez, and Raquel Castro. Next week, America will begin voting on whom they think has "The Voice."

You can reach Alexandra Gratereaux at: Alexandra.Gratereaux@foxnewslatino.com

or via Twitter: @GalexLatino

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