Five debutants to watch in the Tokyo Olympics pool:

Ariarne Titmus announced herself by stunning Katie Ledecky to win the 400m freestyle crown at the 2019 world championships and is in sizzling form to again threaten the American great in Japan.

The 20-year-old, who made her debut for Australia in 2016 but has yet to swim at an Olympics, recently clocked the second-fastest times in history over both 200m and 400m.

Add in a new Australian record over 800m and Ledecky has a serious challenger.

Nicknamed 'The Terminator', Titmus gets in the zone listening to rock music, borrowing her mum's playlist.

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"I'm not usually a rock music fan, but for some reason listening to it loud before I race kind of just gets me going," she said.

Prodigy Kliment Kolesnikov holds world junior records in the 50, 100, and 200m backstroke and has proved he is ready for the big stage as he spearheads the next generation of Russian swimmers.

Just 21, the 6ft 5ins (1.96m) Muscovite is at his first Olympics as owner of the world's best this year in the 100m backstroke and second quickest in the 100m freestyle.

American sprint star Caeleb Dressel and Australian defending champion Kyle Chalmers will be treating him with caution in the blue riband 100m free, while countryman Evgeny Rylov and American defending champion Ryan Murphy await in the back.

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Kolesnikov's recent form shows they have reason to be wary with the Russian rocket capable of challenging and potentially upsetting his more experienced and decorated rivals.

Hungarian poster boy Milak burst on the scene as a 17-year-old at the 2017 world championships on home soil in Budapest, snaring silver in the 100m butterfly behind Dressel and ahead of Rio Olympic gold medallist Joseph Schooling.

It thrust him into the spotlight and a month later he won four gold medals at the world junior championships, also excelling in the freestyle.

He has only got better since, incredibly shattering Michael Phelps' 200m butterfly world record in a sizzling time of 1:50.73 two years ago.

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After his 2020 was derailed by a bout of Covid-19, he rebounded to be the fastest this year (1:51.10) in the 200 fly by a massive three seconds, and is closing in on Dressel's best over 100m to set the scene for a blockbuster Olympic debut.

The 18-year-old American, who has a Chinese-born mother, stamped herself a Tokyo contender with four gold medals at the 2019 junior world championships in Hungary, and has only benefited from the Olympics' one-year postponement.

Small for an elite swimmer at 5ft 8ins (1.7m), Huske says the extra time allowed her to focus on strength training that has helped her late in races.

Highlighting her potential, she clocked the fifth-fastest time in history to win the 100m butterfly at the recent US trials, establishing her as a clear Olympic favourite alongside Australia's Emma McKeon and China's Zhang Yufei.

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"The more pressure there is, I feel like the better I do," said Huske, who credits her mother Ying, who grew up in a Chinese labour camp, as her inspiration.

The 21-year-old Australian boasts an impressive record, holding 26 National Age Championship gold medals along with the 200m freestyle junior world record.

But it was his victory over Olympic 400m freestyle champion Mack Horton at the Australian trials that really turned heads.

Horton was narrowly in front at 300m but Winnington came storming back to touch in a lightning 3:42.65, the world's fastest this year, to make him a genuine gold medal contender.

Winnington, who describes himself as relaxed but sometimes loud, attributes his success to changing coaches last year.

"It means everything to me. I dreamt of this moment as a kid," he said of going to Japan, having also qualified for the 200m freestyle alongside Australian Olympic 100m champion Kyle Chalmers.