Kristyna Pliskova suprisingly lost to Peng Shuai in Nanchang, while Alison Van Uytvanck saw off compatriot Kirsten Flipkens in Hiroshima.
Rain intervened to bring Karolina Pliskova's last-16 clash with Polona Hercog to a halt, with the top-seeded Czech facing a tough battle.
Madga Linette, who lost to Naomi Osaka at the US Open, put in an impressive display as she progressed to the quarters at the Jiangxi Open.
Serena Williams won her first grand slam on September 11 1999, triumphing in the US Open final, and we take a look at her career in numbers.
Serena Williams is agonisingly close to matching Margaret Court's grand slam record but has been stuck on 23 titles for almost three years.
Nina Stojanovic brushed aside second seed Wang Yafan at the Jiangxi Open, while Hsieh Su-wei began her title defence at the Japan Open.
Angelique Kerber was knocked out in a first-round thriller at the Zhengzhou Open, but Jelena Ostapenko survived a major scare.
New world number five Bianca Andreescu is determined to keep winning after her first grand slam success at the US Open.
After an early exit at the US Open, Carolina Garcia was successful in her first outing at the Zhengzhou Open on Monday.