Australian swimmer Kaylee McKeown claimed the women's 100m backstroke gold in an Olympic record time of 57.47 seconds at the Tokyo Olympic Games here on Tuesday.The result was 0.02 seconds behind her own world record, but enough for her to beat second-placed Kylie Masse of Canada, who finished in 57.72 seconds.The bronze went to 19-year-old Regan Smith of the United States.Tom Dean and Duncan Scott led a one-two finish for Britain in the men's 200m freestyle.The 21-year-old Dean sprinted for the gold in one minute and 44.22 seconds, with Worlds bronze medallist Scott 0.04 seconds behind.Brazilian Fernando Scheffer took the bronze in 1:44:66.Russian (ROC) swimmers dominated the men's 100m backstroke as Evgeny Rylov and Kliment Kolesnikov claimed the gold and silver, edging defending champion Ryan Murphy to third.Finishing sixth at Rio 2016, Rylov touched first this time in 51.98 seconds, setting a new European record. His compatriot Kolesnikov was 0.02 seconds behind, taking home the silver in his Olympic debut.World record holder Murphy had to settle for a bronze, unable to catch up with the two Russians after the first 50m, clocking 52.19.China's reigning world champion Xu Jiayu finished fifth in 52.51.Lydia Jacoby of the United States won the women's 100m breaststroke in her Olympic debut. The 17-year-old beat South African Tatjana Schoenmaker to second in the final sprint, clocking one minute and 04.95 seconds for the gold.Schoenmaker, leading for the majority of time, had to settle for silver in 1:05.22. Olympic and world champion Lily King took the bronze in 1:05.54.