SINGAPORE - Two-time women's singles champion Wang Yihan of China and Japan's second seed Nozomi Okuhara were the biggest names to be booted out of the OUE Singapore Open on Thursday.

Wang, the world No. 6, posted a sub-par performance in her match against Thailand's Porntip Buranaprasertsuk. She was beaten 21-9, 24-22, 21-17.

Buranaprasertsuk earns a quarter-final clash against team-mate Ratchanok Intanon.

Japan's Okuhara, the world No. 4, struggled to find a solution against Sun Yu of China, and lost to her lanky opponent 21-16, 21-11. Sun, the defending champion, will play South Korea's Sung Ji Hyun on Friday.

In the men's singles, Chen Long posted another comeback win in his tie against two-time champion Boonsak Ponsana of Thailand. The world No. 1 won 17-21, 21-18, 21-9 to earn his first quarter-final appearance in three appearances in Singapore.

Ponsana, who had made the Singapore final three other times, said he struggled to keep up with his opponent towards the end of the match.

He said: "My level is not enough to beat top players like Chen Long. I try, but I just couldn't."

Two-time Olympic champion Lin Dan strolled into the quarter-finals, beating Indonesia's Jonatan Christie easily 21-13, 21-7. He said: "The draught in the arena today was a bit harder to deal with and it felt like the stadium was a bit colder. I did my best to control my rhythm on court. I didn't give my opponent any chances so I think I fared well."

An all-China semi-finals remains on the card, after Wang Zhengming and Tian Houwei also won their respective matches today.