Japan's 2020 Tokyo Olympics medal hopeful Rikako Ikee picked up her second and third gold medals of the 2018 Asian Games on Monday, winning the women's 50-meter butterfly and 100 freestyle.

The 18-year-old Ikee, who led Japan's women to a win in the 4x100 freestyle relay the previous night, clocked a games record 25.55-second time at GBK Aquatic Center to grab gold in the butterfly.

She stepped to the blocks not too long after and showed great resilience to come from behind to win the 100 freestyle, stopping the clock in 53.27, yet another games record.

"It was good that I was able to come back in the second half of the (100 freestyle) race," she said. "I expected her to come out fast in the first half, but I really put it together after the turn."

"I came in today aiming to get two gold medals and I am happy I could achieve that."

(Ikee (L) powers to victory in the 100 freestyle)

In the butterfly, Ikee led home silver medalist Wang Yichun and bronze medalist Lin Xintong, both from China, and in the freestyle she beat another Chinese pair, Zhu Menghui and Yang Junxuan, respectively.

Kosuke Hagino suffered a shock loss when China's Wang Shun swam over the top of him to steal the Japanese swimmer's 200 individual medley title. The reigning Olympic 200 IM gold medalist led for most of the final lap, but Wang stretched to touch in 1:56.52, 0.23 ahead of Hagino.

Qin Haiyang finished behind Hagino, just beating Japan's Daiya Seto to bronze.

Kanako Watanabe defended her 200 breaststroke title for Japan, beating China's Yu Jingyao with a 2:23.05 time. Watanabe, the 2015 world champion, beat Yu and Japan compatriot Reona Aoki, who finished third to add a bronze to her silver in Sunday's 100 breaststroke.

"First of all, I remained composed and then at the very end I was able to bring it home," said Watanabe. "I am not satisfied with my time. I knew the very end was going to be make-or-break, and that's where my composure paid off."

Hagino made amends in the night's final race by joining up with Naito Ehara, Reo Sakata and Katsuhiro Matsumoto to win the 4x200 freestyle, Japan's fourth gold of the night. China could not match Japan's games-record 7:05.17 time, taking silver while Singapore finished third.

In Monday's opening race, China's three-time Olympic gold medalist Sun Yang won gold in the men's 800. The 2015 world champion over the distance touched in 7:48.36 to beat Japan's Shogo Takeda by nearly five seconds with Vietnam's Huy Hoang Nguyen in third.

Ryosuke Irie won his second silver medal of the games when he was touched out by China's Xu Jiayu in the men's 50 backstroke.

Xu swam 24.75 for the gold with Irie reaching the wall 0.13 seconds later. South Korea's Kang Ji Seok won bronze.