Yamaguchi, the winner of the event in 2016, was beaten 19-21, 18-21 by her unseeded opponent at Odense Sports Park in this BWF Super 750 tournament. 

Cheung’s reward for her surprise win is a second-round clash with three-time world champion and Olympic champion Carolina Marín of Spain.

Marín overcame Thailand’s Pornpawee Chochuwong 21-16, 21-19 today.

Another seeded player exiting the women’s singles at the first hurdle was seventh-ranked Chinese He Bing Jiao, who fell to a 23-25, 18-21 defeat at the hands of South Korea’s Sung Ji Hyun.

There were no such problems, however, for third seed Nozomi Okuhara of Japan and fifth seed PV Sindhu of India.

Okuhara, the 2017 world champion, beat Thailand’s Busanan Ongbamrungphan 18-21, 21-9, 21-16, while Sindhu, the current world champion, defeated Indonesia’s Gregoria Mariska Tunjung 22-20, 21-18.

In the first round of the men's singles event, top seed and defending champion Kento Momota of Japan overcame Wong Wing Ki Vincent.

The world number one, competing after back-to-back tournament victories at the China Open and Korea Open, triumphed 21-15, 21-17.

Next up for Momota is set to be India's Bhamidipati Sai Praneeth after the 2019 world bronze medallist beat two-time Olympic champion and five-time world champion Lin Dan of China 21-14, 21-17.

Sixth seed Jonatan Christie, meanwhile, came from a set down to defeat home player Jan Ø. Jørgensen, the 2010 champion, 20-22, 21-12, 21-11.

The most notable casualty on the opening day of the men’s singles was eighth-seeded Indonesian Anthony Sinisuka Ginting, who lost 21-16, 19-21, 20-22 to France’s Brice Leverdez.

Competition is due to continue until Sunday (October 20).