A 17-year-old Spring Valley sprinter likened to Usain Bolt and a 29-year-old world champion dash man wowed the crowd Saturday at the 65th annual Mt. SAC Relays.

Fred Kerley, who won his title in the 100-meter dash at the 2022 world meet in Oregon, contested his first 400-meter dash since March 2023, winning in 44.73 seconds — top 10 globally this season.

Brandon Arrington Jr., still a junior at Mount Miguel High School, shattered the San Diego County prep record in the 100 with his wind-legal 10.21 at Hilmer Lodge Stadium in Walnut.

Two hours later, still wearing a Nike uniform, Arrington fought a cross wind (amounting to a slight headwind) to scorch the 200 in 20.44 — behind his own county record of 20.35 set a week earlier at the Arcadia Invitational.

“Just get out” fast, he said of his half-lap effort, then “I’m unstoppable. Stayed relaxed, not get tensed up.”

How good are those marks?

The 6-foot-3, 185-pound wide receiver and cornerback would have won the college and elite division 200 Saturday. He broke the Mt. SAC Relays prep record of 10.27 set in 2016 by Michael Norman — later a world 400 champion. His 200 mark erased the Mt. SAC prep record of 20.86 by Nikolas Miller in 2023.

(At Arcadia, Arrington’s 100 bettered the prep meet record held by Noah Lyles, the Paris Olympic gold medalist at 100.)

Asked if he would rather play in the NFL or do professional track, Arrington quickly replied: “Both.”

Supremely confident but with proper “yes, sir” manners, the teen phenom said he’s being recruited by 43 colleges but has a “top 6 right now.”

Edging closer to world-class speed, Arrington said a “sub-20 could be this year or next year or college — it don’t matter. That sub-20 is going to be on my name somehow somewhere.”

A year after Maryland 16-year-old Quincy Wilson won Olympic gold as a member of the 4×400 relay team — and in the wake of 17-year-old Gout Gout setting Australian sprint records this season — Arrington sees the youth movement as a byproduct of better training and technology.

(He says he’s talked to Wilson, a Junior Olympic legend.)

Arrington also credits his Mount Miguel coaches Thomas Tyler and Antoine Woods.

“Yeah, they take it very serious with me,” he said.

Kerley, who won a bronze medal in last year’s Paris Olympic 100, said he used the one-lap race as strength training for the 100 and 200 in which he competes on the new Grand Slam Track circuit.

“Just a workout,” he said of Saturday’s 400 under sunny skies with temps in the low 70s. The 100 “is still my main event.”

But he’s considering changing his “racer” status on the Michael Johnson-founded track league from “short sprints” (100 and 200) to “long sprints” (200 and 400.)

Still, he considers the 400 — once his prime distance — as something that ages his body, while the 100 is something he can do rolling out of bed.

“That’s where God put me in these last couple of years — to give me the opportunity to make all the money in the world I can,” he told Times of San Diego in a quiet hallway inside the stadium.

His return to the 400 wasn’t easy, though.

“I had a hard week this week,” said the Los Angeles-based athlete, coached by USC assistant John Bolton. “Body’s sore right now.”

And he wasn’t sure how fast to go out in the quarter-mile.

So he doesn’t want people to judge him by a time more than a second behind his personal best of 43.64 set in July 2019. (Or his seventh-place finish in the Kingston 100 on April 4.)

His season goals remain the same: “Championship, championship, championship — the best to perform in the championship.” (Tokyo is hosting the world meet in mid-September.)

Young Arrington’s 10.21 smashed the county high school record of 10.30 jointly held by Riley Washington of Southwest High School in 1992 and Kenan Christon of Madison High School in 2019.

His tall frame prompted one meet commentator to note how he was “Usain Bolt-esque getting into the blocks.” (World record-holder Bolt is 6-5.)

Arrington sees himself competing at the 2028 Los Angeles Games.

At Mount Miguel, he also sees a mural depicting 2023 discus world champion Lagi Tausaga, a fellow Matador.

It inspires him.

“Yeah,” he said. “It’s like one day I can be on there, too.”