Surprise star poised to ignite Aussie medal rush

Surprise packet Brendon Smith has emerged arsenic a immense accidental to unafraid Australia's archetypal medal astatine the Tokyo Olympics aft smashing his ain nationalist grounds to suffice fastest for Sunday's 400m idiosyncratic medley final.

Smith, the little-known Victorian, swam a sizzling 4.09.27s to acceptable the gait up of New Zealand's Lewis Clareburt (4:09.49s) and USA's Chase Kalisz 4:09.65s.

The last is scheduled for 11.30am AEST.

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Australia's Brendon Smith fist bumps USA's Jay Litherland aft his sizzling vigor swim. (Getty)

"I privation to spell faster each clip I swim, truthful truly blessed with that and to beryllium archetypal ranked going into the last is truly surreal," Smith said.

"It felt fast, but to spell 4:09.2 is astir apt faster than I thought it was."

Asked if helium could spell faster, the 21-year-old replied: "We'll see."

Daiya Seto of Japan aft his vigor aquatics successful the 400m idiosyncratic medley. (Getty)

Smith's vigor featured golden medal favourite and section leader Daiya Seto, who sensationally bombed retired of the last by 0.32s.

Incredibly, the three-time satellite champion aboriginal claimed helium was cruising but got his calculations wrong.

"Even successful the past hundred, I didn't fto it each out," Seto said done a translator.

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"Even erstwhile the different swimmers were coming adjacent me... 5 years ago, I went excessively accelerated successful the prelims and couldn't spell accelerated capable successful the finals. I tried to debar that."

Australian swimming fable Ian Thorpe described the curveball arsenic a "huge boilover."

Smith's last connected Sunday volition beryllium followed up by the men's 400m freestyle last (11.52am AEST), featuring Australians Elijah Winnington and Jack McLoughlin.

Winnington and McLoughlin shared a dormant heat. (Getty)

The brace finished successful a dormant vigor successful 3:45.20s, which placed them adjacent 4th fastest.

Henning Muhlleitner of Germany qualified fastest successful 3:43.67s.

McLoughlin admitted the vigor aquatics didn't rather spell to plan.

"I thought 3:44 would beryllium wherever we'd request to be."

Mollie O'Callaghan, Meg Harris, Madison Wilson and Bronte Campbell of Australia. (Getty)

But everything went to publication for Australia's ace women's 4x100 freestyle relay team.

Despite missing their 2 fastest sprinters - Emma McKeon and Cate Campbell - the squad of Mollie O'Callaghan, Meg Harris, Madison Wilson and Bronte Campbell - acceptable the fastest clip with 3:31.73s.

The USA squad of Olivia Smoliga, Catie DeLoof, Allison Schmitt and Natalie Hinds precocious successful fifth.

The last is scheduled for 12.45pm AEST connected Sunday, with the Aussies the hottest of favourites.

- With AP