JAKARTA (Kyodo) -- Reigning world silver medalist Yasuhiro Koseki and Olympic bronze medalist Daiya Seto each collected their second gold medals on Wednesday as Japan won four events on the fourth day of Asian Games swimming.
Koseki, who won silver in the 200 breaststroke at the 2017 worlds, shook off a slow morning heat to win the men's 100-meter breaststroke gold from Lane 1 in games-record 58.86 seconds, completing a 100-200 breaststroke double.
"I could not achieve the 58.50-second range that I was aiming for but I swam the first half of the race faster than at any time before," Koseki said after beating China's Yan Zibei by 0.45 second and Rio Olympic gold medalist Dmitriy Balandin of Kazakhstan by 0.53 at GBK Aquatic Center in Jakarta.
With the 50 to come on Friday, the 26-year-old has a chance of taking a hat-trick of medals in the stroke.
Japan saw more gold later when Seto clocked 4:08.79 to beat reigning Olympic champion Kosuke Hagino by 1.51 in the men's 400 individual medley. China's Wang Shun was third.
Seto's gold was his second at this edition of the Asian Games and fourth in total.
"It was so tight my head was pounding, and that was my plan," said Seto. "I have had a lot of comfortable races recently, and all the easy races I have had would make it difficult for me to win gold in Tokyo."
"This was my season's best time, it was a race that makes me think I'll be able to handle the Tokyo Olympics."
Natsumi Sakai won her second gold of the games when she swam a 59.27-second women's 100 backstroke final, adding that title to the 4x100 freestyle relay she won earlier.
The 17-year-old reigning world junior champion over 50 beat her compatriot Anna Konishi by 0.40 and China's Chen Jie by just over a second.
"I am satisfied with my time and since I was aiming for the gold I am so happy," Sakai said. "I knew I couldn't win unless I led out in the first half. The latter half was painful, but it was good that I held on."
Japan continued a superb night in the pool when its men's 4x100 freestyle squad -- made up of Shinri Shioura, Katsuhiro Matsumoto, Katsumi Nakamura and Juran Mizohata -- beat China by half a body-length, claiming the title for the first time in three meets.
The Japanese set a games record of 3:12.68 with Singapore finishing in third.
"I am so happy that I managed to hold off the (Chinese) till the end," said anchor Mizohata, 20. Matsumoto, who also swam well, said, "This will be the start as we aim to compete on the world level."
In the mixed 4x100 medley relay, which will be introduced at the 2020 Tokyo Olympics, China took bragging rights, holding off Japan in with a 3:40.45 time.
Despite a valiant effort by Rikako Ikee, Japan took silver, 0.76 back, while South Korea placed third.
"I am frustrated that we couldn't win," said Ikee, who failed to win a gold on Wednesday, her first day of futility at these games.
Earlier, Olympic men's 100 butterfly champion, Joseph Schooling of Singapore, took the gold in a games record 51.04-second time.
China's Li Zhuhao finished second and Japanese veteran Yuki Kobori won bronze, his fifth Asian Games medal and second here after his gold in the 4x200 freestyle.
China's Li Bingjie won a tight women's 200 freestyle, establishing her winning margin with a strong final 50 meters as she held off compatriot Yang Junxuan.
Yang stretched to the wall just 0.01 ahead of Japan's Chihiro Igarashi, who won her first individual medal of the games in Indonesia.
In the women's 200 butterfly Zhang Yufei was too fast for the Japanese pair of Sachi Mochida and Suzuka Hasegawa. The Chinese swimmer touched in 2:06.61 with the silver and bronze medalists both more than 2 seconds adrift.