TOKYO, July 24 (Reuters) - Japan suffered an opening swimming session blow on Saturday when top gold medal hope Daiya Seto failed to make the men"s 400 metres medley final, while Britain"s Adam Peaty admitted that winning his 100m breaststroke heat had not felt like an Olympic experience. The 27-year-old Seto, world champion and top ranked in the event, finished ninth in the heats. He was the bronze medallist in Rio five years ago and favourite to win gold in Sunday"s final before his shock exit. "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 200 metres 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. Australia"s Brendon Smith was fastest in the medley 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. Britain"s Max Litchfield pipped Seto to eighth place by three tenths of a second. In the breaststroke, defending Olympic champion Peaty was fastest in qualifying ahead of his closest challengers, Dutchman Arno Kamminga and American Michael Andrew. "We will see where we are tomorrow (Sunday)," said Peaty. "There are a lot of variables at the Olympics that you can’t control. It was delayed. It’s hot... It’s really weird with no crowds so that’s one thing we have to psychologically adapt to. "It doesn’t feel like the Olympics," added the Briton, who said he considered the pool to be ideal for quick times. China"s Zhang Yufei tied with Australia"s Emma McKeon to go through fastest for the women"s 100m butterfly semi-finals in 55.82, followed by defending champion Sarah Sjostrom of Sweden in 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 in 3:43.91, with the top-ranked Australians Elijah Winnington and Jack McLoughlin safely through to Sunday"s final both with 3:45.20. Emma Weyant of the United States was the top qualifier in the women"s 400m medley with 4:33.55, the fastest time in the world this year, almost two seconds ahead of next fastest Aimee Willmott of Britain. World record holder and reigning champion Katinka Hosszu of Hungary scraped through in seventh in 4:36.01 looking well below her best as she finished behind her 17-year-old compatriot Viktoria Mihalyvari-Farkas. Australia"s crack women"s team were fastest in the 4x100m freestyle relay, finishing 1:78 seconds ahead of the Netherlands with Canada third.