Venus Williams returns to Lucie Safarova of the Czech RepublicAHMED JADALLAH/Reuters
Second-seeded Petra Kvitova and fourth-seeded Ana Ivanovic followed defending champion Venus Williams to an early exit at the Dubai Tennis Championships on Wednesday.
In all, five of the top eight seeded players failed to reach Thursday's quarterfinals: Kvitova, Ivanovic, No. 5 Agnieszka Radwanska, No. 7 Angelique Kerber and No. 8 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 93 degree F (34 C) temperatures.
"I think she played awesome," Williams said. "There were a couple of games there that I didn't even get my racket on the ball. What can I say to that?"
Williams offered Safarova six opportunities to break serve and the Czech player took advantage four times, twice in each set.
"I was firing the ball, serving really well," Safarova said. "I put the pressure (on) right away from the first point. My lefty serve into her body and mixing the lefty serve with the really flat and fast serves, that seems (to) give her a little trouble."
Joining Williams on the sidelines was fifth-seeded Agnieszka Radwanska, who lost to unseeded Garbine Muguruza of Spain 6-4, 6-2.
Radwanska was broken five times.
"I think when you're not playing your best tennis then it's hard to compete with those kind of players," Radwanska said. "I think I didn't serve well enough to win that."
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.