Ahmed Hafnaoui won Tunisia's first gold at the Tokyo Olympic Games in the men's swimming 400m freestyle here on Sunday.The 18-year-old pushed Australia's Jack Mcloughlin to second in the final sprint, becoming an Olympic champion in his first appearance in three minutes and 43.36 seconds, 0.16 second ahead of the Aussie.Kieran Smith won a bronze for the United States in 3:43.94.Japanese swimmer Yui Ohashi claimed the women's 400m individual medley title and burst into tears after winning in four minutes and 32.08 seconds. Emma Weyant (4:32.76) and Hali Flickinger (4:34.90), both from the United States, took the silver and the bronze respectively.Rio Olympic champion Katinka Hosszu of Hungaria finished fifth in 4:35.98.Meanwhile, American swimmer Chase Kalisz touched home first in four minutes and 09.42 seconds to clinch gold in the men's 400m individual medley. This is the first swimming gold for Team USA in Tokyo.Kalisz' compatriot Jay Litherland finished second in 4:10.28. Australia's Brendon Smith took the bronze 0.1 second after Litherland.