Second-seeded Petra Kvitova and fourth-seeded Ana Ivanovic followed defending champion Venus Williams to an early exit at the Dubai Tennis Championships.
In all, five of the top eight seeded players failed to reach Thursday's quarter-finals: Kvitova, Ivanovic, fifth-seed Agnieszka Radwanska, seventh-seed Angelique Kerber and eighth-seed Williams.
Kvitova, the reigning Wimbledon champion, went down 6-3, 4-6, 6-3 to 13th-seeded Carla Suarez Navarro, while Ivanovic fell to 17th-seeded Karolina Pliskova 6-2, 4-6, 6-4.
Suarez Navarro pulled out of the Antwerp final this past Sunday with a neck injury, but appears in fine form this week.
Top-seeded Simona Halep and third-seeded Caroline Wozniacki will be in third round action later.
Williams, with three career titles in Dubai, lost 6-4, 6-2 to 11th-seeded Lucie Safarova.
The eighth-seeded Williams looked listless in the humid 34C temperatures.
Joining Williams on the sidelines was fifth-seeded Agnieszka Radwanska, who lost to unseeded Garbine Muguruza of Spain 6-4, 6-2.
Elsewhere, seventh-seeded Angelique Kerber was ousted by 10th-seeded Flavia Penetta 6-2, 3-6, 6-1 and sixth-seeded Ekaterina Makarova of Russia defeated Zarina Dyas of Kazakhstan 6-3, 6-4.