DUBAI, United Arab Emirates (AP) 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.

By contrast, top-seeded Simona Halep and third-seeded Caroline Wozniacki scored straight set victories to advance.

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.

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 Radwanska, who lost to unseeded Garbine Muguruza of Spain 6-4, 6-2.

''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.''

Halep ousted Tsvetana Pironkova 6-4, 6-3, while Wozniacki beat 15th-seeded Alize Cornet, last year's finalist, 6-4, 6-0.

Halep, who lost her serve on double faults in the first game of both sets, said she was unaware of all the seeded players that lost ahead of her on Wednesday.

''It doesn't matter sometimes who wins or who lose, because tennis, it's like you never know what is happening on court,'' Halep said. So, I take every match like a tough one and I expect everything.''

Wozniacki knew of the upsets. Nevertheless, she wasn't concerned she might suffer the same fate.

''I think the players that won, it's not like they come out of nowhere,'' Wozniacki said. ''Most of these girls have had a good year or are very high in the rankings. It happens at big tournaments like this.''

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.