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The Games started with Japan’s 8-1 win over Australia in the opening round of the women’s softball tournament.
The match kicked off at 9 a.m (0000 GMT) in Fukushima, the city hit hard by the tsunami-caused meltdown at the nuclear power station in 2011.
Three softball and six women’s football matches are scheduled in total for Wednesday, two days before Friday’s opening ceremony of the Tokyo Games.
Also in action is the U.S women’s football team, with the world champions seeking revenge against Sweden after they lost to the Swedes in the 2016 quarter-finals.
Japan won the last Olympic softball tournament in 2008.
The sport was dropped at the 2012 and 2016 Games and will also not feature in 2024.