Results from the WTA clay court tournament in Stuttgart on Friday (x denotes seeding): Quarter-finals Ashleigh Barty (AUS x1) bt Karolina Pliskova (CZE x6) 2-6, 6-1, 7-5 Elina Svitolina (UKR x4) bt Petra Kvitova (CZE x7) 6-7 (4/7), 7-5, 6-2 Simona Halep (ROM x2) bt Ekaterina Alexandrova (RUS) 6-1, 6-4 afp