By Lerpong Amsa-ngiam
The eighth-ranked Ratchanok, who won this tournament in 2016, rallied back from a poor start to beat Han Yue of China 19-21 21-11 21-13 in the second round on Thursday.
Yamaguchi had a much easier time as she cruised past Chua Huo Zhen Grace of Singapore 21-6 21-11.
The Japanese third-seeded player leads the head-to-head series against the Thai 12-9. She beat Ratchanok 16-21 21-14 25-23 in their latest shodown during the German Open final last month.
While there’s no other Thai singles players left in the tournament, two doubles teams of the Kingdom still remain.
Fifth-seeded Jongkolphan Kititharakul and Rawinda Prajongjai take on Liu Xuanxuan and Xia Yuting of China in women’s doubles quarter-finals.
In mixed doubles, Dechapol Puavaranukroh and Sapsiree Taerattanachai will play Pranaav Jerry Chopra and Reddy N. Sikki of India.