Third seed Ratchanok Intanon suffered a shock 21-15, 14-21, 18-21 loss to unseeded South Korean Kim Ga-Eun in the first round of the Malaysia Masters in Kuala Lumpur on Wednesday.
The Korean needed 59 minutes to finish off the Thai who won the tournament in 2018 and 2019. Ratchanok, 28, was also crowned champion at the Malaysia Open last year.
Fifth seed Pornpawee Chochuwong defeated Sung Shuo-yun of Taiwan 22-20, 21-15 in the women's singles competition.
The Thai next meets Michelle Li of Canada in the second round (last 16) of the US$420,000 tournament.
They have not met since 2019 but Li has a 2-1 head-to-head lead over the Thai.
Eighth seed Busanan Ongbamrungphan had few problems against Myanmar's Thet Htar Thuzar, winning 21-12, 21-8.
Busanan will take on Yvonne Li from Germany for a place in the quarter-finals.
Top seed Akane Yamaguchi of Japan cruised past India's Akarshi Kashyap 21-17, 21-12.
In the men's singles, Thailand's eighth seed Kunlavut Vitidsarn beat Kanta Tsuneyama of Japan 21-15, 21-19.
He next meets India's Srikanth Kidambi in the last-16 round.
Kidambi defeated France's Toma Junior Popov 21-12, 21-16 in the opening round.
Sitthikom Thammasin lost to Denmark's Magnus Johannesen 22-20, 10-21, 9-21.
Kantaphon Wangcharoen was defeated by Indonesia's Christian Adinata 21-16, 21-17.
In the mixed doubles, Thailand's second seeds Dechapol Puavaranukroh and Sapsiree Taerattanachai defeated Tang Chun Man and Tse Ying Suet of Hong Kong 21-15, 21-18.
Supak Jomkoh and Supissara Paewsampran also advanced after edging past Malaysia's Tan Kian Meng and Lai Pei Jing 22-20, 22-20.