After a few weeks of blind auditions, NBC's "The Voice" launched its battle rounds on Monday night. The premise is simple: Two teammates at a time perform a duet in a boxing ring-style stage. One is declared the winner, while the other is sent home, unless other coaches decide to steal the losing artist for themselves.

Monday's episode also introduced this season's mentors. Adam Levine was assisted by OneRepublic's Ryan Tedder; Cher helped out Team Blake Shelton; Christina Aguilera was joined by Ed Sheeran; and Cee Lo Green welcomed R&B star Miguel.

Here's a rundown of what happened:

The first battle round pit Team Adam's Nic Hawk and the female wedding singer known only as Grey against each other. Adam assigned them the Jessie J hit "Domino" because they are such an eclectic pair. Blake and Cee Lo both loved Nic's energy and gave him a vote of confidence. Christina preferred Grey's consistency on vocals. Adam echoed Christina's opinion and declared Grey the winner. Calling Adam "an idiot," Blake immediately stole Nic and added him to his team.

Next up was Team Christina's Amber Nicole and Timyra-Joi, who tackled Beyoncé's "Listen." Christina was brought to tears by what she heard from her artists. Blake remarked that he'd never seen Christina cry on the show, and added that she had a tough decision on her hands. Christina named Amber the winner of the battle. It was the end of the road for Timyra-Joi.

Two Team Blake contestants, Justin Chain and Shelbie Z, were given the country song "Don't You Wanna Stay" by Jason Aldean and Kelly Clarkson. Cee Lo said the artists delivered a beautiful rendition. Blake picked Shelbie Z, and Justin was eliminated.

Recent high school grad Anthony Paul and 17-year-old Caroline Pennell of Team Cee Lo sang a stripped-down version of the Justin Bieber dance-pop hit "As Long as You Love Me." Adam said he sided with Caroline because she made the song different. Adam and Christina both thought it was the best battle round up to that point. Cee Lo praised Anthony's natural talent, and said Caroline took him to another place as an artist. Caroline advanced, and Christina stole Anthony.

Donna Allen, a 54-year-old former member of Gloria Estefan's Miami Sound Machine, battled Jamaican singer Tessanne Chin for Team Adam. They did a duet of Emili Sandé's "Next to Me." Christina said Tessanne carried the song to another level. Adam called them both "world-class singers" who have the ability to win the competition. Tessanne prevailed, and Donna was dismissed.

Christina selected The Animals' "House of the Rising Sun" for Briana Cuoco - the sister of "The Big Bang Theory" star Kaley Cuoco - and high school junior Jacquie Lee. Kaley was spotted in the audience for this battle round. Cee Lo described the battle as "amazing." Blake said Briana delivered "power and precision," and favored her. Christina opted for Jacquie. Blake and Cee Lo both made a bid to steal Briana. It was her choice, and she went with Blake.

The battle rounds continue on "The Voice" Tuesday night at 9 p.m. ET, following the season premiere of "The Biggest Loser."