Japan surged into the lead in gold medals Tuesday with 10 through Day 4 of the 2020 Tokyo Olympics.

The host country took the gold medal in softball, defeating the United States 2-0 in the championship game. With that silver medal, the Americans lead the overall standings with 25 medals: nine gold, eight silver and eight bronze.

China is second overall with 21 medals: nine gold, five silver and seven bronze. Japan, which also has won three silver and five bronze medals, is tied for third with the Russia Olympic Committee (seven gold, seven silver, four bronze) with 18. Five of Japan's gold medals have come in judo.

Tuesday's Tokyo highlights included:

--The Russia Olympic Committee team upset the United States to win the women's gymnastics team final. The Americans won the silver medal, despite the loss of star Simone Biles, who stepped away from the competition after the first rotation when she realized, she said, she wasn't in "the right headspace." Great Britain took the bronze for its first medal in the event in 93 years.

--Marketa Vondrousova of the Czech Republic ousted four-time Grand Slam winner Naomi Osaka of Japan 6-1, 6-4 in the third round of the tennis tournament. In the women's draw, No. 4 Elina Svitolina is the highest remaining seed.

--Lydia Jacoby, a 17-year-old from Alaska, was a surprise gold medalist in the 100-meter breaststroke, winning the race in 1:04.95. Silver medalist Tatjana Schoenmaker of South Africa was 0.27 seconds back, followed by defending champion Lilly King of the United States. Jacoby is the first-ever Olympic swimmer from Alaska -- a state with just one 50-meter pool.

--The United States won bronze medals in the men's and women's 100m backstroke. 2016 Rio Games winner Ryan Murphy had the top time in qualifying but was third behind Russians Evgeny Rylov (51.98 seconds) and Kliment Koleskinov (52.00) with his time of 52.19. Kaylee McKeown of Australia set a women's Olympic record as she won gold in 57.47 seconds, followed by Canadian Kylie Masse (57.72) and American teen Regan Smith (58:05).

--Swiss women swept the mountain bike competition. Jolanda Neff completed the approximately 12-mile course in 1:15:46 to take gold, with her teammates Sina Frei and Linda Indergand more than a minute behind.

--Carissa Moore defeated South African Bianca Buitendag to win the women's shortboard event as surfing made its Olympics debut. Moore, of Hawaii, was the top seed. Amuro Tsuzuki of Japan won bronze.

--In the women's triathlon, Flora Duffy of Bermuda finished in 1:55:36 to win gold. She was followed by Georgia Taylor-Brown of Great Britain and American Katie Zaferes.