Top seed Tanongsak Saensomboonsuk was bundled out of the Thailand Open in Bangkok on Friday, beaten in three games by fellow Thai Pannawit Thongnuam.
In the first meeting between the two players, unseeded 21-year-old Pannawit secured a surprising 21-17, 17-21, 21-18 victory to book his place in the semi-finals.
Tanongsak looked to have found a way back into the match after losing a tight first game by winning the second, but he was totally outplayed in the decider.
Pannawit moves on to face third seed B. Sai Praneeth, after the Indian defeated Kantaphon Wangcharoen 21-16, 21-17.
The second semi-final sees fourth seed Jonatan Christie of Indonesia take on Malaysian Joo Ven Soong.
In the women’s draw, top seed and home favourite Ratchanok Intanon stayed on course for the title after beating countrywoman Nitchaon Jindapol 21-13, 21-15.
Next up for the former world champion is American Beiwen Zhang.
The other semi-final sees second seed Saina Nehwal of India take on Thai fourth seed Busanan Ongbamrungphan.