Australia's world champion Ariarne Titmus edged world record holder Kathleen Ledecky of the United States to claim gold in the women's 400m freestyle at the Tokyo Olympic Games here on Monday.The Aussie beat Ledecky to second in the last 100m, winning in an Olympic record time of three minutes and 56.69 seconds. Rio Olympic champion Ledecky took silver in 3:57.36 and China's Li Bingjie bagged the bronze.Li set a new Asian record at 4:01.08, thanks to a 29.47-second final lap that saw her overtake Canadian Summer McIntosh.The United States triumphed in the men's 4x100m freestyle relay, claiming gold in three minutes and 08.97 seconds, reports Xinhua.The team, comprising Rio champions Caeleb Dressel and Blake Pieroni, Bowen Becker and Zach Apple, enjoyed a safe lead and retained the title for Team USA.Italy finished second in 3:10.11. Australia surged from sixth to third 0.11 seconds behind Italy, thanks to a fastest 46.44-second split by Kyle Chalmers.Rio Olympic champion Adam Peaty defended his title in men's 100m breaststroke here on Monday, winning the gold medal in 57.37 seconds.The three-time world champion had a convincing lead over silver medallist Arno Kamminga of the Netherlands, who finished 0.63 seconds behind.The bronze went to Italian Micolo Martinenghi. The 21-year-old touched home in 58.33.Margaret MacNeil of Canada touched home first in 55.59 seconds to win the women's 100m butterfly gold.Fresh from winning silver in women's 4x100m freestyle on Sunday, the 2019 world champion edged China's Zhang Yufei by a close 0.05 seconds to win her maiden Olympic title.Zhang, finishing first in the semifinals, settled for silver in 55.64 seconds. Australia's Emma McKeon, who finished eighth at 2016 Rio, took a bronze 0.08 seconds further behind.