Tony Stewart, bothered by a back injury sustained last weekend at Darlington, vowed before Sunday's Food City 500 not to quit.
But the pain, and the pounding that Bristol Motor Speedway dishes out, were too much. He reluctantly got out of his car late after spinning his Pontiac.
"Guys, I'm tired," he said over the radio. "I'm not 100 percent right now, I'm sorry if I'm letting you down."
Asked if he wanted to be replaced by Todd Bodine, the relief driver on standby in his pits, Stewart sadly said yes.
Stewart was hooked to a back stimulator he could control himself. He worked his way to the front and led 74 laps but had fallen to third when he began to wear down.
Stewart spun on Lap 365 and got out right after. He was helped from the car and was wobbly as he was taken for treatment.
Bodine got on the track in 21st and finished 15th.
EYE ON HARVICK: Kevin Harvick will be penalized this week for his pit road confrontation with Greg Biffle after Saturday's Busch Grand National race, NASCAR president Mike Helton said Sunday.
Helton had a long discussion with Harvick and car owner Richard Childress before the Food City 500 about the incident.
Childress is confident his 26-year-old driver will not be suspended for his actions after the Channellock 250, but Helton would not indicate what the penalty will be.
"I think the issue we have to deal with is how disruptive Harvick's actions were and how detrimental his actions were to the overall scheme of things," Helton said.
The confrontation began after Biffle hit Harvick's car with nine laps left, ending Harvick's race. During a subsequent interview, Harvick made it clear he would be waiting for Biffle when he got out of his car.
Harvick waited atop a pit box and watched Biffle pull onto pit road after the race. He jumped down, sprinted to him and leaped over a barrier and the car to get to Biffle. Harvick grabbed Biffle's fire suit and yelled at him, but no punches were thrown.
Childress agreed NASCAR must take action against his driver.
"They can't just let it become a free-for-all; they have to have some kind of control," he said. "How they control it, it has to be up to them."
STAYING PAT: Sterling Marlin was 19th, a finish that snapped his streak of eight top 10s, but he retained his lead in the points.
Marlin, 99 points ahead of Matt Kenseth, cut a tire while running in the top five on Lap 310 and pitted under green. He fell a lap behind and never recovered.
"Me and Mark Martin got together when I was passing him and that cut down a right rear tire," Marlin said. "You're going to have some cut tires, so hopefully we've got that behind us now."
_ TIMES WIRES