Dubai - Karolina Pliskova and Garbine Muguruza re-established order among seeds on Wednesday as both reached the quarter-finals of the WTA Dubai Championships.
Top seed Simona Halep plays her opener later against fan favourite Ons Jabeur of Tunisia.
Muguruza had to struggle two days after beating Kim Clijsters in the Belgian's first WTA match since 2012 after announcing a surprise comeback aged 36.
She will bid for a semi-final place on Thursday, taking on Jennifer Brady, a 4-6, 6-4, 6-1 winner against Marketa Vondrousova.
Aryna Sabalenka (BLR x7) bt Elise Mertens (BEL) 6-4, 6-3
Petra Martic (CRO x8) bt Barbora Strycova (CZE) 6-3, 6-3