The duo were mentored by Jewel and Lionel Richie before performing the song 'Chain of Fools' in an attempt to make it to the live shows.
Watch Sera and Geoff's battle below:
Cee Lo Green began the coaches' comments and said he was "pleasantly surprised", adding that the "energy was very high". However, he added that he would choose Geoff.
Meanwhile, Blake Shelton suggested that both Sera and Geoff can "sing the crap out of this song" and are "giving [it] everything they've got", while Adam Levine praised Geoff's spontaneity.
Aguilera had the final say and began by praising the "power" in Geoff's voice, adding that she has a lot of "respect" for Sera as a vocalist.
"You know I love you both and I love the growth that you both have shown me," she continued. "But honestly I've got to go with my gut - the winner is Sera."
Speaking to social media correspondent Christina Milian backstage, Geoff revealed that he hurt his knee before the performance and admitted that the battle was "nervewracking".
"But you know, we walked out there to do what we do and that is our love and passion for music," he said. "Sera and I had talked time and time again - it didn't seem like a battle, it was a duet. Two voices that came together. And I think Christina did a great job picking the song."
Meanwhile, Sera suggested that she has made a "lifelong friend" in Geoff, adding: "I learned so much from Geoff. He is just the most upstanding, genuine person... I couldn't have asked for a better person."
The Voice airs on Mondays at 8/7c on NBC.
Watch Sera and Geoff talking to Christina Milian below: