The Tokyo Olympics suffered its first major shock on Saturday night when Japanese world champion Daiya Seto failed to qualify for the 400m individual medley final.
Victorian 21-year-old Brendon Smith emerged as a shock gold medal contender, breaking the Australian record to qualify fastest for the final.
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But the bigger shock was the fact that Seto - the top ranked swimmer in the event - failed to make the final altogether.
The 27-year-old was the bronze medallist in Rio five years ago and favourite to win gold in Sunday's final.
Seto made the final turn in first place but ran out of gas in the final 20 metres, finishing fifth in his heat.
"I miscalculated and didn't put everything into the race like I did in Rio," Seto said.
The Japanese hope will also compete in the 200m butterfly at the Tokyo Aquatics Centre and said he would need to refocus quickly.
"I will just have to put this out of my mind," he added.
Seto has had a tumultuous 12 months, resigning as captain of the Japanese swim team after an extramarital affair late last year.
Smith was fastest with a time of 4:09.27, followed by New Zealand’s Lewis Clareburt and American Chase Kalisz in what proved to be a highly competitive heat.
Whatever happens in Sunday’s final, a new champion will be crowned.
Reigning gold medallist Kosuke Hagino opting out of the event to focus on the 200m medley.
Fans and commentators were left in disbelief over Seto's extraordinary fail.
Emma McKeon qualifies fastest for 100m butterfly semis
Meanwhile, Emma McKeon tied with China's Zhang Yufei to go through fastest for the women's 100m butterfly semi-finals in 55.82, followed by defending champion Sarah Sjostrom of Sweden on 56.18.
“The adrenaline was pretty high being my first race and my first race of the Olympics," McKeon said.
“I felt it went pretty well.”
Germany's Henning Bennet Muhlleitner qualified fastest in the men's 400m freestyle in the third-fastest time in the world this year, finishing in 3:43.67.
He was followed by Austrian Felix Auboeck 3:43.91, with the top-ranked Australians Elijah Winnington and Jack McLoughlin safely through to Sunday's final both with 3.45.20.
Australia's dominance of the women's freestyle relay continued despite the absences of McKeon and flag-bearer Cate Campbell in the heat team.
Mollie O'Callaghan, Meg Harris, Madi Wilson and Bronte Campbell still booked lane four, in a time almost two seconds ahead of the next-best the Netherlands.
Australia's star attractions McKeon and Campbell, who hold the fastest 100m freestyle times in the world this year, will race in Sunday's final with Wilson and triple Olympian Bronte Campbell.
McKeon's relay final will follow her 100m butterfly semi-final, with compatriot Brianna Throssel sneaking into those semis as 16th qualifier.
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