Hailey Steele and Leland Grant, who we met on tonight's episode of 'The Voice,' have an interesting relationship as pop country duo the LiNE. They met when he was hitting on her at a bar, offering up a shot of Jack. Though their relationship didn't blossom romantically, they hit it off as pals and became writing partners, then eventually a singing duo. The best way to describe their bond isn't brother-sister, according to Steele, who says, "We're more like an old married couple."

The LiNE didn't go country on tonight's show, but performed Tom Petty and the Heartbreakers' 'American Girl,' winning over not only America, but also the entire panel of 'The Voice.'

Blake Shelton's eyes lit up when he heard them, and he hit his button almost immediately, not even realizing there were two artists until he turned around. Christina Aguilera caught on quickly, as Cee Lo Green and Adam Levine each sang along. During the breakdown, the other three judges finally came around -- first Xtina, then Cee Lo, then Levine. The crowd went absolutely nuts!

"Individually, each singer has to hold their own," Adam told the young duo. "The energy changed in the room. I want to be part of that energy ... please!"

Instigator and would-be matchmaker Cee Lo was nosier. "You guys are a couple?" he asked. When they denied it, he laughed, "Not yet." Then he got down to business: "Great performance, great song choice. I enjoyed it."

Aguilera wasn't letting them go without a fight. "I know something's amazing when I hear it," she said, "and I heard that with you guys. I could tell you guys were having fun up there." To rub her opponent's nose in it, Xtina brought up the duet act that Shelton sent home last year. Cold!

Naturally, Shelton brought up his wife Miranda Lambert and their duets together, and the fact that he was first to choose the pair. Levine wouldn't give up so easily, urging them, "Sometimes the less obvious choice is the one you should go with."

They went with an even less obvious choice: Aguilera, who cackled in the panel's face. This clearly bugged Shelton, who had some very sour grapes. "I actually feel bad for them for that," Shelton said. "I think they were fooled by flash and boobs."

Watch the LiNe Perform 'American Girl' on 'The Voice'