- Karolina Pliskova awaits in last eight after beating Donna Vekic
- Elena Rybakina retires injured against Beatriz Haddad Maia
Defending champion Iga Swiatek made a winning return to the WTA Tour with victory over Zheng Qinwen in Stuttgart.
The world No 1 pulled out of the Miami Open and Billie Jean King Cup duty with Poland because of a rib injury, but eased to a 6-1, 6-4 success against her Chinese opponent to reach the quarter-finals of the Porsche Tennis Grand Prix.