The Voice: Kelsea Ballerini fills in as guest coach for Kelly Clarkson

Surprise guest coach Kelsea Ballerini sat in for an ailing Kelly Clarkson on Monday's first Battle Rounds episode of The Voice on NBC.Although Kelly, 38, had tested negative for coronavirus, strict on-set guidelines meant that the coach had to watch her team from home.Country-pop artist Kelsea, 27, had previously served as an advisor for Team Kelly and toured with the talk-show host, so she felt she knew what Kelly wanted. 'Just pretend I'm Kelly!' Kelsea joked to her new castmates.Asked if he had any advice for the guest coach, John Legend, 42, said, 'No! We're still trying to defeat you Kelsea, as though you were Kelly Clarkson.' Nick Jonas, 29, said that Blake Shelton, 44, would no doubt try to get the upper hand.'In all the advice I've gotten from Kelly, the main one is, ''Keep the rivalry going'',' Kelsea acknowledged. 'I like this show better already with you here instead of Kelly,' Blake teased.Team Kelly's first battle paired two pop singers with a delicate touch: Gean Garcia, 19, from New York City, and Ryleigh Modig, 18, from Spencer, Massachusetts.Kelly had them sing Ariana Grande's POV, and chose as their mentor Despacito hitmaker Luis Fonsi, 42. 'I am so impressed with the level of artistry,' Luis said after his first listen. 'I did not see that coming.'On performance day, a sick Kelly called in to tell Kelsea that Gene and Ryleigh were one of her best battles, and added, 'If I could give you any advice: 'Don't. Trust. Blake.'Onstage, the contestants were evenly matched, and Blake crowed, 'I love that this is [Kelsea's] first battle.' Kelsea noted that Kelly was sad not to see the singers in person, but 'I'm super-stoked that I can.''Since I'm keeping this seat warm for Kelly, I'm going to call her,' Kelsea added, ringing the coach.When Kelly picked up, she immediately apologized for pairing Gean and Ryleigh but reassured Kelsea, 'You should feel safe picking whoever, 'cause I don't think either one of them is going home.' 'Kelly sounds just fine to me,' cracked Blake, who sat nearby. 'She's laughing, she's talking… I think I heard ocean waves in the background.'After some deliberation, Kelsea saved Ryleigh, who 'nailed every note,' while Gean was stolen by John.The EGOT winner immediately crooned the 'Team Legend' song that he sang to all of his contestants. 'You know I had to steal for you,' John warbled. 'Kelly didn't even show up for you. It's Gean and John Legend!'Team Blake was next to do the battle rounds, with mentoring from country artists Dan Smyers and Shay Mooney, aka Dan + Shay.Blake chose two very different men to sing the rockabilly-flavored Waylon Jennings' tune Ain't Living Long Like This: Connor Christan, 23, from Gallipolis, Ohio, and Aaron Konzelman, 39, from Waco, Texas. After their performance, Kelsea noted that Aaron had a wonderfully smoky rasp.She also told Connor that his fiery take made it seem like he was giving his own concert.Blake saved Connor, admiring how much work he'd been putting into