Second seed Dimitrij Ovtcharov was sent crashing out of the International Table Tennis Federation Bulgaria Open as he was beaten by Chinese world number 111 Zhao Zihao in Panagyurishte.
The German recovered from being two games down but the unfancied 22-year-old Chinese player dug deep to secure an 11-6, 12-10. 8-11, 11-6, 5-11, 11-9 victory.
He will face Quadri Aruna in tomorrow's semi-finals after the Nigerian edged a thriller 4-3 against Jun Mizutani of Japan.
In a topsy-turvy encounter Aruna progressed 8-11, 11-9, 6-11, 12-10, 11-9, 4-11, 13-11.
Harimoto Tomokazu won an all-Japanese last eight battle 11-7, 11-6, 14-12, 7-11, 13-11 against compatriot Takuya Jin
Marcos Freitas of Portgual awaits in the last four after defeating Chih-Yuan Chuang of Chinese Taipei 3-11, 11-2, 11-3, 11-13, 4-11, 11-5, 11-9.
Women's top seed Kasumi Ishikawa of Japan was knocked out in straight sets as China secured three of the four semi-final berths.
Ishikawa lost 10-12, 5-11, 9-11, 4-11 to He Zhoulia in just under 39 minutes.
Compatriot Mima Ito progressed to the women's singles quarter-finals against Singaporean Yu Mengyu by virtue of an 11-5, 11-8, 6-11, 11-6, 11-8 scoreline.
She will face Chen Xingtong of China in the last four after she won 11-6, 11-8, 11-2, 11-4 against Jeon Ji-hee of South Korea.
Xingtong's compatriot Wu Yang progressed to the semi-finals after Hitomi Sato of Japan withdrew from their quarter-final clash.
Japanese duo Jun Mizutani and Ito won gold in the mixed doubles final.
They defeated Ma Te and Wu Yang of China 11-8, 12-10, 9-11, 11-9.