Nishiya topped a youthful podium with Rayssa Leal of Brazil, also 13, taking the silver medal and Japan's Funa Nakayama, 16, winning bronze. With an average age of 14 years and 191 days, it is the youngest individual podium in the history of the Olympic Games.
The youngest-ever Olympic champion is Marjorie Gestring, who won the springboard title at the 1936 Berlin Games at the age of 13 years 267 days, just 63 days younger than Nishiya.
The host nation has enjoyed a clean sweep of golds in the street event of skateboarding after Yuto Horigome won the men's competition.
Nishiya stumbled and missed the landing on her first two tricks but nailed her final three to finish with a score of 15.26, topping Leal's tally of 14.64, and beamed with delight when her gold medal win was confirmed.
At 13 years and 203 days, Leal would have become the youngest individual Olympic champion had she won.
Women’s Olympic #skateboarding street podium:— Olympics (@Olympics) July 26, 2021
?? Nishiya Momiji: 13 years old
?? Rayssa Leal: 13 years old
?? Nakayama Funa: 16 years old
Gestring's record still could still be toppled at this Games, however.
Sky Brown, at 13 years and 28 days, will become Britain's youngest Olympian when she competes in the women's park skateboarding on Wednesday, 4 August.
Japan's Kokona Hiraki (12 years and 343 days) is also competing in the same event.
Skateboarding is one of five new sports added for this Games, with the street course emulating the urban environment as tricks are performed on benches and rails.
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