LONDON -- Manteo Mitchell heard the POP! and knew it wasn't good. "It felt like somebody literally just snapped my leg in half," he said.

The American sprinter had 200 meters to go in the first leg of the 4x400-meter relay preliminaries Thursday and a decision to make: keep running or stop and lose the race. To him, it was never much of a choice.

He finished the lap and limped to the side to watch the Americans finish the race and qualify easily for the final. A few hours later, doctors confirmed what he suspected: He had run the last half-lap with a broken left fibula.

"I heard it and I felt it," Mitchell told The Associated Press. "But I figured it's what almost any person would've done in that situation."

Mitchell finished his heat in a more-than-respectable 46.1 seconds, and the United States tied the Bahamas in the second heat in 2 minutes, 58.87 seconds -- the fastest time ever run in the first round of the relay at the Olympics.

The 25-year-old sprinter from Cullowhee, N.C., said he was diagnosed with a complete break of the left fibula -- but it was not a compound fracture and the bone is expected to heal on its own in four to six weeks.

He knew what the stakes were when he lined up to run the first leg of his first Olympics. The Americans have won gold in the last eight long relays they've entered at the Olympics.

"Even though track is an individual sport, you've got three guys depending on you, the whole world watching you," Mitchell said. "You don't want to let anyone down."

He said he slipped on the stairs a few days ago in the athletes village but didn't think much of it. Training went well and he felt good when he lined up to kick things off for the Americans. He said he was feeling great, as well, when he looked at the clock while approaching the 200-meter mark, somewhere in the high-20 or low-21-second range.

"I was doing my job," Mitchell said. "But probably at 201 meters, I heard it and I felt it."

He credited something more than simple adrenaline for pushing him the rest of the way around the track.

"Faith, focus, finish. Faith, focus, finish. That's the only thing I could say to myself," he said.

Mitchell was a promising high school football player at Crest High School in Shelby, N.C., when another broken bone altered his career. He broke his left arm, and his coaches -- seeing the natural talent -- pushed him over to the track.

Western Carolina coach Danny Williamson saw Mitchell finish second several times to a future Olympian, Travis Padgett, and offered a scholarship.

"He was a team person here," said Williamson, who received the first call from Mitchell after he got off the track Thursday. "As soon as he came to Western Carolina, no matter what the situation, he'd do anything we asked of him."

On the world's biggest stage, Mitchell took the team-first thing to a whole new level.

He is the 2012 version of Jack Youngblood, the Rams linebacker who played the Super Bowl on a broken leg. Or Tiger Woods, who won the 2008 U.S. Open on a broken leg. Or, maybe most appropriately, Kerri Strug, whose vault on a sprained ankle sealed the first-ever Olympic team gymnastics gold for U.S. women at the 1996 Atlanta Games.

"I don't know how you write this, but I'd like to believe the only way he would have stopped is if the leg had fallen off," Williamson said.

Mitchell will spend the rest of the Olympics, and beyond, in a walking boot and on crutches. He'll be at the stadium to watch Friday's final.

The United States is no shoo-in to win a medal this time, because LaShawn Merritt and Jeremy Wariner -- Olympic gold medalists in 2004 and 2008 -- are also both out with injuries. But the medals ceremony is Saturday, and if the U.S. finishes in the top three, Mitchell would get one, too, since he ran in the preliminaries.

Forgive him if he doesn't leap onto the podium, though.

"I pretty much figured it was broken, because every step I took, it got more painful," he said. "But I was out there already. I just wanted to finish and do what I was called in to do."