EUGENE, Ore.—Everything is golden for Sanya Richards-Ross, for a change.

Richards-Ross, known as much for her heartbreaking losses in the biggest races and her battle with a rare disease as for her dominance of the 400 meters, will get another shot at an Olympic gold medal. She won her signature event Sunday at the U.S. Olympic Track and Field Trials in a world-leading time of 49.28.

Her husband, NFL cornerback Aaron Ross, provided reassurance by looking her in the eyes and saying, “Execute.” Ross then watched his wife run a flawless race, passing the 200 mark with the exact split her coach prescribed and pulling away in the last 60 meters. Richards-Ross, who grew up in Pembroke Pines, still had enough energy to blow kisses to the crowd and jog a lap waving an American flag.

Her performance was one of the highlights of seven finals on Day 3, the first day of sunshine at the trials, although cool temperatures persisted in the mecca of the sport, known as Tracktown, USA.

One of the lowlights was Walter Dix’s last-place finish in the men’s 100 meters. Fort Lauderdale’s Dix, bronze medalist in the 100 and 200 at the 2008 Olympics, pulled up after his semifinal heat, clutching his left hamstring. He was not a factor in the final, won by Justin Gatlin in 9.80 seconds.

“Things happen,” a stone-faced Dix said afterward, his leg wrapped in a bandage. “I can’t say much about the injury. I have to have it checked. Hopefully, I will heal up and get back for the 200.”

Dix, 26, who switched his training base from Tallahassee to join the star-studded stable of sprinters under coach John Smith at UCLA, has had hamstring problems all season. He said the pain surfaced in the semifinals. Dix had supplanted Tyson Gay as the top American speedster, but Sunday’s final turned out to be a comeback showdown for second-place finisher and Clermont, Fla.-based Gay, who had hip surgery last year, and Gatlin, who served a four-year doping suspension two years after winning gold at the 2004 Athens Olympics.

A decision on how to resolve Saturday’s tie for third place in the women’s 100 meters led to more uncertainty. Jeneba Tarmoh, initially announced the winner of the photo finish, and Allyson Felix, who crossed the line in the identical time of 11.068, could be headed for an unprecedented run-off. Or they could break the tie with a coin toss. Or one could decline her spot.

It’s up to them, but it has to be settled before the meet ends on Sunday, July 1. Only the top three finishers make the U.S. team headed to the July 27-Aug. 12 London Olympics. Both Tarmoh and Felix plan to run the 200 meters; the women’s final is Saturday. If both athletes agree to a coin toss or a run-off, that’s how the tie will be broken. If they disagree on the procedure, or refuse to declare their preference, it will be broken by a run-off, which has been used in U.S. swimming trials before. If the run-off ends in a dead heat, it will be broken by a coin toss.

The finish line image, recorded at 3,000 frames per second, showed the torsos of Tarmoh and Felix hitting the line at the same instant. At first, Tarmoh was announced the winner, and she was led to the press room to tell the media about her happiness at making her first Olympic team. Felix, four-time 200-meter world champion who had added the 100 to her Olympic program, was in tears. Twenty-four hours later, after a tie-breaking procedure had been created during improvised meetings by USA Track and Field officials and athletes and the U.S. Olympic Committee, their fates were still up in the air. They may opt to see how they fare in the 200; qualifying rounds start Thursday. They train together under coach Bobby Kersee, who will add his input.