Denny Hamlin says a simple set-up misstep was the cause of his surprise struggle in qualifying for the NASCAR Sprint Cup Chase round at Loudon.
The Joe Gibbs Toyota driver, who finished a close second when the series visited the one-mile oval in July, started the weekend strongly by topping first practice.
He was then drawn last for qualifying, leading several drivers to cite him as a pre-qualifying favourite.
Hamlin could not match such a billing however, with his best effort enough only for 32nd on the grid, his worst start all season.
The 31-year-old said his team had mistakenly filled his tyres to race, rather than qualifying, pressure.
"Holy cow, I knew something had to be wrong," he said. "It looked like... we just ended up having race pressures, we didn't put our qualifying pressures in, so that was a tough one.
"I knew something was really, really wrong because the car was bobbing down real bad."
Hamlin refused however to be downbeat following the mistake, saying he was confident he could rebound in the race.
"[It's a] simple mistake," he added. "We'll rebound from it - we're quick enough. It's frustrating, but we'll get them.
"If there was nothing wrong then I would really be shaking my head, [but] at least we identified what the problem was."