Ratchanok Intanon and Busanan Ongbamrungphan advanced to the last 16 of the US$420,000 BWF Indonesia Masters in Jakarta on Wednesday.
World No.13 Ratchanok defeated Huang Yi-hsun of Taiwan 21-11, 21-17 while Busanan came through her match against fellow Thai Pornpawee Chochuwong at the World Tour Super 500 event.
Ratchanok is the only champion from the inaugural edition in 2010 to be in this year's draw. She won the tournament when she was 15.
She will play seventh seed Zhang Beiwen of the US for a place in the quarter-finals.
Busanan advanced after Pornpawee retired in the second game. Busanan won the first 21-19.
World No.19 Busanan will play sixth seed Han Yue of China in the last 16.
In other matches involving Thai players on Wednesday, Supanida Katethong and Kantaphon Wangcharoen both went out in the first round.
Men's singles player Kantaphon went down to third seed Anthony Ginting of Indonesia 13-21, 15-21 while Supanida was beaten by Natsuki Nidaira of Japan 21-23, 7-21 in the women's singles opener.
Mixed doubles duo Ruttanapak Oupthong and Jhenicha Sudjaipraparat lost to Goh Soon Huat and Shevon Jemie Lai of Malaysia 15-21, 15-21.
In late matches, world champion Kanlavut Vitidsarn was to play Wang Tzu-wei of Taiwan while women's doubles pair Jongkolphan Kititharakul and Rawinda Prajonghai were to face Kaitlyn Ea and Gronya Somerville of Australia.
Meanwhile China's Lu Guangzu claimed the day's biggest upset after knocking out fourth seed Jonatan Christie of Indonesia 19-21, 21-19, 21-19.
Lu will play Kiran George in the last 16 after the Indian beat Toma Junior Popov of France 18-21, 21-16, 21-19.