Sixth seed Pornpawee Chochuwong came from behind to upset fourth seed Ratchanok Intanon in an all-Thai quarter-final at the Korea Open in Suncheon on Friday.
Pornpawee, 22, defeated the former world champion 18-21, 21-12, 21-13 in a battle of players who have just recovered from Covid-19.
Both missed last month's All England Open after testing positive for Covid-19.
In Saturday's semi-finals of the World Tour Super 500 event, Pornpawee meets unseeded South Korean Kim Ga-Eun who comfortably beat Malaysia's Goh Jin Wei 21-15, 21-18 in the last eight.
Kim stunned China's Olympic champion Chen Yufei in the previous round.
In another women's singles quarter-final, PV Sindhu proved too strong for Busanan Ongbamrungphan.
The Indian third seed defeated the seventh-seeded Thai 21-10, 21-16.
Sindhu next faces a tough assignment against second seed An Se-Young of South Korea who saw off Japan's Saena Kawakami 21-14, 21-7.
In the women's doubles quarter-finals, eighth seeds Benyapa Aimsaard and Nantakarn Aimsaard of Thailand defeated South Koreans Kim Min-Ji and Seong Seung-Yeon 21-11, 22-20.
The Thai duo meet South Korea's Chang Ye-Na and Jung Kyung-Eun for a place in the final.
The Koreans beat compatriots Jang Eun-Seo and Kim Hye-Rin 30-29, 21-17, 21-12 in the quarter-finals.
In the men's singles, Thailand's eighth seed Kunlavut Vitidsarn lost to Indonesia's third seed Jonatan Christie 21-8, 17-21, 19-21.
Christie will meet India's Kidambi Srikanth in the semi-finals. Srikanth rode on his power and precision to outwit local hope Son Wan-Ho 21-12, 18-21, 21-12.
The tournament ends on Sunday.