Tai Tzu-ying
In July, she won the Japan Open, her second Japan Open title since her first six years prior. That same month, she won a match against Taiwanese competitor Tai Tzu-ying, the highest-ranked player in the world, placing her in the finals of her first Indonesia Open. In August, Yamaguchi was defeated in the second round of the 2019 BWF World Championships held in Basel, Switzerland, by 20-year-old Yeo Jia Min of Singapore 0–2.