She has beaten kids, and she has beaten women 10 or 15 years her senior. She has beaten Olympians and girls who don’t belong in the same pool with her. She beats top-ranked high school boys in practice pretty much every day, and regularly posts times in her best events that would place her in the middle of the pack on the men’s side. But Friday morning, Katie Ledecky achieved a new, if somewhat esoteric, milestone:

She tied Michael Phelps.

Granted, their heats in the 400-meter freestyle preliminaries at the Arena Pro Swim Series meet were some 35 minutes apart — Ledecky in the women’s event, of course, and Phelps in the men’s — but when the timers had all clicked their stopwatches and the official Omega Timing results were posted, they had clocked in with the exact same finish, right down to the hundredth of a second: 4 minutes 2.67 seconds.

For Ledecky, the time — in the event for which she is the women’s world record-holder — was good enough to seed her first in Friday night’s finals, where she posted a 4:01.95 to win by nearly nine seconds, her third win of the meet. The time was the second-fastest in the world this year, trailing only her 4:00.47 in Austin in January.

For Phelps, the time — in an event he hadn’t contested in nearly six years and entered here on something of a lark — placed him 17th in a 50-man field, and he didn’t even bother swimming in the “C” consolation final Friday night. Instead, he visited the Universal Sports booth during Ledecky’s race and jokingly suggested he and Ledecky should have a match race to break their morning tie.

Katie Ledecky warms up before swimming in the 1,500 freestyle on Day 1 of the Arena Pro Swim Series Mesa at the Skyline Acquatic Center. (Chris Coduto/Getty Images)

“Okay,” Ledecky responded from the pool deck after her victory. “Want to go in an hour?”

“How about now,” Phelps joked, “while you’re tired.”

Whether you are the most decorated Olympian of all-time, or a once-a-week summer league swimmer, there is never any shame in being beaten — or in Phelps’s case, tied — by Ledecky. The 18-year-old from Bethesda, a three-time All-Met Swimmer of the Year, is widely considered the best female swimmer in the world at the moment, and getting better.

Just before this week’s Mesa meet, Ledecky joined some other Team USA members — male and female — at the Olympic Training Center in Colorado Springs for 2 1/2 weeks of high-altitude training. Whenever it came time for some “threshold” sets, it was considered a given that Ledecky would keep up with, or in some cases beat, some of the top male swimmers in the country.

“She did some ridiculous stuff up there,” said Conor Dwyer, a gold medalist at the 2012 London Olympics in the 4x200-meter freestyle relay. “She was on our heels going some times that Ryan [Lochte] and I were going. I’ve never seen a female do that before. . . . I haven’t seen any female train as hard as her. She’s got a work ethic like none other.”

Training with — and racing against — men is nothing new for Ledecky. In fact, Bruce Gemmell, at the Nation’s Capital Swim Club, has long made a point of grouping her with mostly boys during training sessions back home, if only because there were no girls who could push her the way he wanted her pushed.

“Part of what has made her so successful is the boys she trains with,” Gemmell said. “They’re some of the best high school boys in the country. She’s just one of the guys in training. Some days she wins, some days they win. But she’s competing with them every day. There’s no animosity, just competitiveness. She wants to win.”

In an elite swimmer’s internal body clock, where the cycles run in quadrennials, the April of an Olympic off-year is a time of intense workouts and experimentation, as the focus turns to August’s world championships in Kazan, Russia, and further ahead, to the 2016 Rio de Janeiro Olympics.

“It’s a really exciting time right now, just over a year from the Olympic Trials . . . and 100 days until the world championships,” Ledecky said. “Things are coming up quickly, and these meets are really good at setting you up for the next meet. I take each meet as a stepping stone and find ways to improve from training.”

To that end, Ledecky is swimming both the 100 and 200 freestyles this week — with one eye toward earning spots on the United States’ freestyle relays a year and a half from now — as well as the 400 individual medley, which she says she likes to race “once a year, for fun.” On Thursday night, she won the women’s 200 free, but finished fifth in the 400 IM.

By late summer, as Russia beckons, the fun will be over, the training will be tapered, the times will start to fall, and the best female swimmers in the world — and a sizeable number of men, too — will be trying their best not to get blown out of the water by Katie Ledecky.