Athing Mu strode calmly amid her competitors to the starting line Monday, straight to Lane 7, and plopped her oversized backpack into the basket provided. There was only one problem, explained by the No. 6 sticker on her left leg: Lane 7 belonged to Hanna Green. Mu burst out laughing and moved her gear one spot over.

“Something always happens every race. I’m so upset they got that on camera!” Mu said afterward, covering her megawatt smile with a hand in faux embarrassment.

It may have been the one time all night at the U.S. Olympic track and field trials when a rocket-legged teenager showed their age. Even on a night when newly minted five-time Olympian Allyson Felix returned to the track and advanced out of the 200 meters first round, youth seized the spotlight on the fifth day of competition at the trials in Eugene, Ore.

Both running their first professional races, both trying to make their own brand of history, Mu, 19, and 18-year-old men’s 1,500 hopeful Hobbs Kessler played starring roles at Hayward Field — with 18-year-old Nico Young qualifying for the final of the men’s 5,000 meters late at night, on the heels of heat winner and 2016 silver medalist Paul Chelimo.

In the first professional race of her career, Mu dominated her 800-meter heat in 2:00.69, finishing in the place she has grown accustomed to. Since she emerged in her early teens on the track scene in New Jersey, where her parents moved 20 years ago from Sudan, Mu’s career has been a ceaseless string of broken records. She won the NCAA title in the 400 and broke two outdoor collegiate records at Texas A&M.

“Being a prodigy is something I’ve always wanted to be,” Mu said. “It’s awesome to be called that.”

Mu — it’s pronounced Uh-thing Mo — ran with composure beyond her years, her head barely bobbing as her long strides powered her twice around the oval, leading the whole way and fending off any challenge without stress. She is just as poised off the track, flashing her vibrant personality and smile. A moderator at her post-race news conference complimented the colors of the apparel brand she had chosen.

“You know what?” Mu said. “Don’t I look good in blue?”

Underscoring the prevalence of youth, Mu was not even the youngest runner in her event. That was Juliette Whittaker, a 17-year-old from Laurel, Md., who also advanced to the next round. She finished third in her heat and qualified on the strength of a 2:01.21 time, a personal best.

In the men’s 1,500, Matthew Centrowitz, the reigning Olympic champion from Arnold, Md., cruised through to the semifinals. Kessler’s professional debut managed to draw more attention than even the gold medal winner.

Kessler won the night’s first heat by staying calm and waiting until just the right moment to burst to the head of the pack. With about 100 meters left, Kessler was trapped on the inside behind a pack of six runners. He slowed down to open space, scooted to the outside and kicked hard to finish, leaning at the line to win a slow-paced heat in 3:45.63.

“At 100 to go, I knew I had it,” Kessler said. “Before that, lack of experience, I didn’t know how stuff was going to work.”

Kessler, who is from Ann Arbor, Mich., turned professional this week and said he still cannot process that he runs for a living. He seems to toggle between enjoyment and seriousness. Asked for his preparation between Thursday and the semifinals, Hobbs said he would play Mario Kart on his Wii. But he also came to win.

“The real day is Sunday,” Kessler said. “I came to make the team. … I’m out here just having a good time. This is like the most important race of their life, and I’m just out there going after it. It’s a little bit more fun I would say.”

Reigning world champion DeAnna Price threw the hammer just once, and her 252-foot 11-inch heave — a trials record — was all she needed to finish qualifying ranked first. Price has dominated a strong field of U.S. hammer throwers, having won the past two national championships and setting a personal best in April that made her the third-best all-time in the event.

The year has been more difficult than Price has made it look. Early in 2021, Price fell ill with stomach issues and lost 10 pounds in a week. She visited multiple doctors and hospitals and never did determine what had happened to her. When she got her coronavirus vaccine, she felt beaten down for two months.

“It’s been a hard battle,” Price said. “I’m finally starting to feel better.”

Price, one of the most effusive figures in the sport, took the pandemic hard for other reasons, too. Her husband, J.C. Lambert, who is also her coach, had to keep telling her to stop trying to embrace their neighbors as they trained outside.

“I really love hugs,” Price said. “I love people.”

In the final event of the night, Emma Coburn claimed a victory for experience. Coburn shaved nearly eight seconds off her 3,000-meter steeplechase trials record by finishing in 9:09.41, advancing to her third Olympics in a dramatic race. The latest berth carried extra meaning after Coburn’s mother was diagnosed in 2019 with Stage 4 cancer.

“Sharing this with my mom is everything,” Coburn said on NBC.

The race also produced one of the most devastating moments of the trials. Leah Falland was in third and running strong with two laps to go before she tripped on her landing over a barrier. Falland tried to recover but missed out on qualifying for what would have been her first Olympics at age 29. At the finish line, as Coburn hugged the second- and third-place finishers, Falland cried, down on all fours.