Katie Ledecky qualifies for another Olympics, but an Australian challenger has emerged

Five years ago in Rio de Janeiro, Katie Ledecky did something no woman had ever done before, and something that no woman has done since: She swam the 400-meter freestyle in 3 minutes and 56.46 seconds. It was an Olympic record, a world record, and good enough for gold in a race that wasn't particularly close. Ledecky won it by almost five full seconds.

On Monday night, Ledecky qualified for another Olympic Games in the same event. But this time, she'll have a challenger.

Halfway across the globe, one day before Ledecky swam the 400 in 4:01.27 at U.S. Olympic trials in Omaha, Ariarne Titmus, a 20-year-old from Tasmania, swam it in 3:56.90 down under. Her time at Australian Olympic trials was just 0.44 seconds off Ledecky's best-ever mark, and more than four seconds faster than Ledecky's Monday time.

Also on Monday, Titmus came 0.11 seconds away from a world record in the 200 free, another Ledecky event.

In doing so, she announced herself as Ledecky's primary competition at the Tokyo Olympics next month.

Ledecky remains an overwhelming favorite in the 800- and 1,500-meter freestyle events, which she'll swim later this week at U.S. trials. She won the 800 by more than 11 seconds in Rio, often swimming in the opposite direction of her peers because she was so far ahead of them. At world championships in 2017, she won the 1,500 by more than 19 seconds.

But as event lengths get shorter, margins narrow, and Ledecky becomes mortal. She's the reigning gold medalist in the 200 and 400 free, but settled for silver in both events at 2019 worlds while battling an illness.

And the 200 and 400 happen to be Titmus' best races. (She'll swim the 800 at Australian trials, as well.) She won the 400 at worlds in 2019, becoming the first woman to beat Ledecky to the wall in a distance event at a major international meet. Her 200-free time on Monday, 1:53:09, was the second-fastest ever, and 0.64 seconds better than Ledecky's top mark (from 2016).

And Titmus did all of this at Aussie trials while battling shoulder soreness.

Ledecky was asked at a news conference on Saturday whether the Australian trials times would get through to her.

“I haven't really thought about it,” she said. “I actually didn't even realize that they were at the exact same time as ours, or I guess a day earlier than us, until maybe yesterday.

“So, honestly, I mean, I'm not going to be checking results every couple hours or anything. I'm sure we'll hear about certain things because I'm sure we'll be asked about certain things, but I think my focus is on Omaha. It's not on anything else. I mean, the medals aren't given this week, so I don't think we have to get too caught up in what times people are going here versus anywhere else in the world right now.”

Ledecky was pleased to "check the box" and officially make the team on Monday. She admitted she was "a little surprised" that her time wasn't faster. But it certainly doesn't mean she'll be four seconds off Titmus' pace in Tokyo.

Ledecky, a 24-year-old freestyle phenom, could be in the mix for six medals in Tokyo — in the 200, 400, 800, 1,500, 4x100 relay and 4x200 relay. She swam five of the six in Rio, winning four golds and one silver. The sixth, the 1,500, was finally added to the Olympic program for 2020 (now 2021).

If Ledecky takes gold in all six, she'd become the winningest female Olympian ever.

American teenage talent wows at Olympic trials

Elsewhere at U.S. Olympic trials, there are young Americans making waves, as well. In Monday's first final, Torri Huske, an 18-year-old from Arlington, Virginia, and Claire Curzan, a 16-year-old from Cary, North Carolina, went 1-2 in the 100-meter butterfly and qualified for Tokyo. They beat out Kelsi Dahlia, who represented the U.S. in the event in Rio.

Huske broke her own American record with a time of 55.66, the fastest in the world this year, and just 0.18 seconds off the world record. She was beaming and borderline speechless during a post-race interview.

"It's really surreal," she said of being Tokyo-bound. "I can't really believe it's happening."

Curzan, meanwhile, became the youngest girl to make the U.S. Olympic swimming team since Ledecky went to London 2012 at age 15.

Neither Huske nor Curzan would've qualified for Tokyo had the Games been held in 2020 as scheduled. But the postponement to 2021 gave both an extra 12 months to mature; to add strength and speed. A year later, they'll be medal contenders.

Curzan will also swim the 100- and 200-meter backstroke, and the 50- and 100-meter freestyle at trials. Huske is also a contender to make the team in the 50- and 100-meter free, and the 200-meter individual medley.

And in 100-meter breaststroke semifinals on Monday night, 17-year-old Alaskan Lydia Jacoby swam a 1:05.71, one second off reigning gold medalist Lilly King's semifinal time, and just 0.34 seconds behind King's training partner, Annie Lazor, who finished second in the semis.

Finals are Tuesday night. Jacoby likely won't touch King, but will have a chance to top Lazor and join Huske and Curzan as teenagers in Tokyo.

Michael Andrew makes his first Olympics by the slimmest of margins

On the men's side, 22-year-old Michael Andrew, eight years after becoming the youngest American swimmer to ever turn pro, qualified for his first Olympic team — barely.

Andrew swam the 100 breast in 58.73 seconds, beating Andrew Wilson by 0.01 seconds and Nic Fink by 0.07. He went slower than he had in prelims, but held on to win, and let out a loud "WOOO!" from the wall.

Andrew, once billed as a potential Michael Phelps successor, began swimming professionally at age 14. His road to the Olympics turned out to be much bumpier than he and many outsiders expected. He trained, unconventionally, with his father in their backyard pool in Kansas, then relocated with his family to California in 2018.

He fell two places short of Rio at trials in 2016. Five years later, he got his moment, and celebrated with his mother. He, like Huske, called it "surreal." So much at Olympic trials is.

More from Yahoo Sports:

• Haynes: CP3 shows his MVP skills in sweep of Jokic, Nuggets

• Nets’ betting odds dramatically change after Kyrie injury

• Eisenberg: Djokovic gave pricey gift to fan at French Open

• Thamel: Marinatto’s legacy isn’t collapse of Big East