The American sprinter had half a lap to go in the first leg of the 4x400-meter relay preliminaries Thursday and a choice 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 200 metres 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 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 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 metres, 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.
A broken bone got him into athletics in the first place.
He was a promising American football player at high school until he broke his left arm and his coaches pushed him toward the track.
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 medallists 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."