Elizabethton scored the go-ahead touchdown in the final minutes to hand Sullivan South its first loss of the season, 28-27 in Kingsport.
Sullivan South led 19-7 at halftime, but in the third quarter Elizabethton quarterback Caleb Bailey kept the ball for a short touchdown run to cut the lead to 19-14.
They later grabbed a 21-19 lead after an Ethan Thomas touchdown run.
The Rebels struck back, as Sullivan South quarterback Dylan Wieger found Evan Headrick on a short touchdown pass to retake the lead 27-21.
But in the final minutes, Bailey found Jeremiah Turner for the game-winning touchdown pass, to make it 28-27.
"For once in my life, I'm speechless," Elizabethton head coach Shawn Witten told News 5 WCYB.
"What can you say about this football team? We fought all the way to the end. Tremendous game on both sides. Our kids never quit, our kids kept their poise, their confidence and we just kept playing until the end."
Both teams enter the playoffs after a 9-1 regular season.