EUGENE, Ore. (AP) Allyson Felix ran through the pain.
Sanya Richards-Ross couldn't overcome it.
And, in the strangest twist of all, Friday night's biggest track news came 3,000 miles away from the U.S. Olympic Trials, when a tweak in Usain Bolt's hamstring threatened to derail the Jamaican champion and change everyone's Olympic math.
On a night Felix successfully auto-piloted her injured right ankle through 400-meter qualifying to keep her chance at a 200-400 double alive, Richards-Ross bid a tearful adieu to the fans, after pulling up 250 meters into her lap around the track - her hamstring too tight to carry on.
''I've had an amazing career,'' the 31-year-old Richards-Ross said. ''To have my last race be here, at Hayward Field, in front of these fans, it's incredible.''
But it was Bolt's hamstring that had the track world buzzing. At Jamaica's national championships in Kingston, Bolt never even made it to the track, pulling out with what he called a minor hamstring injury.
Unlike the United States, where the top three finishers in each event qualify for the Olympics with no exceptions, Bolt can still make it to Rio if he can prove he's fit. That test will come July 22 at a meet in London.
Possibly the biggest beneficiary of Bolt's absence would be Justin Gatlin, the American who has been the Jamaican's biggest challenger the past few years.
''He will be on the Olympic team,'' Gatlin told The Associated Press. ''I don't see him missing out. He's going to do what he needs to do.''
Gatlin starts qualifying in the 100 on Saturday.
Richards-Ross, meanwhile, will have to settle for some fond memories and a heartfelt goodbye to her fans.
In addition to her four Olympic gold medals, including the individual title at the London Games, Richards-Ross holds the stadium record in Eugene - better known as Track Town USA. It was here, five weeks ago at the Prefontaine Classic, that fans got their first true glimpse of what might be coming. Richards-Ross finished seventh that day.
In this one, her first 15 steps out of the blocks were smooth, but she quickly slowed from a sprint to a trot. By the time she hit the first curve on the backstretch, she was jogging. And then she pulled up completely.
''Let's be honest, I hurt my hamstring real bad,'' she said. ''I worked with a great doctor just to get out on the track today.''
After she pulled up, Richards-Ross walked to the finish line. Fans rose from their seats and Richards-Ross blew kisses.
She earned as many of those fans through her failures as her successes - her long battle with illness and injuries, her third-place finish in Beijing that left her weeping underneath the stands, then, finally, the gold medal in London.
''Most fans have seen my heart through my running,'' Richards-Ross said. ''I don't win every time I step on the track. I don't deserve the ovation because I'm always a champion. But I think they see my heart, my determination, my desire to be a good person.''
Now, though, they'll be watching Felix and others finish up the 400.
Felix finished second in her heat, posting a time of 51.96 seconds, then headed straight to the trainer's room for treatment.
She hurt the ankle in the spring and has had a rough time coming back - forced to do most of her running the wrong way around the track so as not to put the injured ankle at more risk.
She has less than 18 hours to recover. Her semifinal heat is set for Saturday afternoon.
Other headlines from Day 1 at track trials:
RUPP ROMP: Galen Rupp won the 10,000 meters in a time of 27 minutes, 55.04 seconds and is now qualified for both the 10K and the marathon. Rupp, the silver medalist at 10K in London, beat Shadrack Kipchirchir by more than 6 seconds. Leonard Korir also qualified. Rupp said he'll also race in the 5K and then decide which races to enter at the Olympics.
SHOT PUT: Adam Nelson was honored for his Olympic gold medal - the one he won in 2004 - during a ceremony before the shot put finals. Wearing a ''Best Dad Ever'' T-shirt with unicorns and a rainbow, the 40-year-old got the ceremony that didn't take place when he was upgraded from silver to gold because of a doping positive. But Nelson, who came out of retirement for trials, did not make the 2016 Olympic team. He finished ninth. The top three were Ryan Crouser, world champion Joe Kovacs and Jordan Clark.
WAIT AND SEE: After making it easily through his first heat in the 400 meters, LaShawn Merritt said he was in ''Wait-and-See'' mode about trying to add the 200 to his schedule. Merritt has the world's fastest time at 200 meters this year, but has never run the distance in a major meet. He said he'll see how he feels when the 400 is over before he decides about the 200.
RETIRING TYPES: 40-year-old high jumper Amy Acuff, a five-time Olympian, failed to qualify and said this was her last meet. Sprinter DeeDee Trotter is also calling it quits - just not quite yet. The 33-year-old, who has two Olympic gold relay medals, made it through 400-meter qualifying but said she'll be hanging it up whenever this season ends.
AP Sports Writer Pat Graham contributed to this report.