Naturally, it was a night he'll never forget.
"Oh, wow! That was my biggest overall college experience, going in in a game-time situation," he said. "I was in the first game (a 63-7 blowout of Western Kentucky) towards the end but it just wasn't as serious because this game they (Bobcats) still had a chance to come back."
The middle linebacker has a key role in Tennessee's defensive scheme. He calls the defensive signals and makes sure everyone in the front seven is aligned correctly. He also has pass-coverage responsibilities for the deep-middle third of the field. Mitchell-Thornton had the added pressure of trying to replace a team captain in Reveiz.
"I had to go in there and try to fill the shoes Nick left behind," he said. "It was a great moment to go in there and be able to control the defense and play SEC football."
Still, advancing from third-team to first-team in a matter of hours was shocking, especially since he began the night stuck behind the seemingly indestructible Reveiz.
"It caught me and pretty much everybody else on the team by surprise," Mitchell-Thornton said. "Most people on the team call him 'The Robot.' It was like, 'Nick hurt? Really? Could somebody give him some oil, so he can keep on going?' Everybody was just totally shocked."
Although he was not mentally prepared to be thrust into a tight game, Mitchell-Thornton had no time to think about that. In retrospect, that may have worked in his favor.
"It wasn't even a thinking moment," he recalled. "It was just like, 'OK, Nick's down and Herman's hurt, so I'm next. I've just got to go in there and handle everything I can, not think about anything else.'"
Junior Savion Frazier moved over from weakside linebacker this week in practice and likely will start at middle linebacker Saturday night against Auburn. Still, Mitchell-Thornton is sure to get plenty of snaps in a backup role. The Vols will need his size (6-1, 229 pounds) in the middle of the run defense against an Auburn offense that ranks No. 5 nationally at 261.2 rushing yards per game.
Like the 5-10, 220-pound Reveiz, Mitchell-Thornton offsets any physical limitations he might have with boundless energy and a tireless work ethic.
"I'm hungry," he said. "I'm a freshman, and I have this big opportunity in front of me - be the Mike linebacker at a big SEC school - so I think hunger and passion is what I bring to the table."
He's hoping that hunger and passion can offset his utter lack of experience and knowledge. He's also hoping to pick Reveiz's brain in the days and weeks ahead.
"I texted him Sunday morning to see how his MRI went," Mitchell-Thornton recalled. "I told him, 'You know you're going to have to help me a lot.' ... I'm hoping I can fulfill the standards he set at the Mike position."