Fighting in the under 59 kilograms Greco Roman event at the Daulet Sports Center in the Kazakhstan capital, Ota triumphed 7-4 against the odds.

He then produced two back-arching throws to beat South Korea's Kim Seung-Hak and make the final.

It meant the 22-year-old Nippon Sports Sciences University qualified for Rio 2016 along with China's Wang Lumin.

“My only thought before the match was, ‘Just do it’,” Ota said.

“I knew it was going to be a tough match, but I just wanted to keep the pressure on him.

“I’m so happy with the win and now I want to focus on winning an Olympic medal."

Wang won a nail-biting final after the duo were initially tied, 8-8.

A good day for Japan continued as they secured two other qualification berths for Rio 2016, with both finalists qualifying in each weight division.

National team newcomer Rei Higuchi qualified in the under 57kg division, gaining a 4-0 final win over South Korea's Yun Jun-Sik.

World Championships silver medalist Sosuke Takatani also qualified in the under 74 kilograms category after a 4-2 win over Uzbekistan's Rashid Kurbanov.

He then withdrew through injury in the final to gift victory to Galimzhan Usserbaev of Kazakhstan.

Mongolia's Sumiya Erdenchimeg trumphed in the under 53kg women's category with an 8-2 victory over Nguyen Thi Lua of Vietnam.

A second home victory came via round-robin format in the women's under 69kg with Elmira Sysdykova winning four times to finish in the gold medal position ahead of fellow qualifier, Chen Wen-ling of Chinese Taipei. 

Peng Fei of China won in the under 85kg Greco Roman event after an 8-2 final victory over Yanarbek Kenzheev of Kyrgyzstan.