Dubai, United Arab Emirates (SportsNetwork.com) - Top seed Simona Halep eased into the quarterfinals, while second-seeded Petra Kvitova and defending champion Venus Williams went by the way of upsets at the Dubai Tennis Championships.

Eleventh-seeded Czech Lucie Safarova upended the eighth-seeded former world No. 1 Williams 6-4, 6-2 at Aviation Club Tennis Centre.

"She is a player who hits the ball a little bit different. I don't think I was playing badly," said Williams.

The 34-year-old Williams is a three-time Dubai champ who beat France's Alize Cornet in last year's finale.

Meanwhile, the French Open runner-up Halep handled Bulgarian Tsvetana Pironkova 6-4, 6-3 and 13th-seeded Spaniard Carla Suarez Navarro stunned the Wimbledon titlist and 2013 Dubai champion Kvitova 6-3, 4-6, 6-3. Suarez Navarro reached a final in Antwerp last week, but was unable to play in the match because of a neck injury.

In some other third-round action involving seeds, No. 3 U.S. Open runner-up and former top-ranked star and 2011 Dubai champion Caroline Wozniacki tackled a 15th-seeded Cornet 6-4, 6-0 and No. 17 rising Czech Karolina Pliskova upset fourth-seeded former world No. 1 Ana Ivanovic 6-2, 4-6, 6-4.

Also on Day 4, talented Spaniard Garbine Muguruza ousted fifth-seeded 2012 Dubai titlist Agnieszka Radwanska 6-4, 6-2, sixth-seeded Ekaterina Makarova doused Kazakhstan's Zarina Diyas 6-3, 6-4 and 10th-seeded Flavia Pennetta foiled seventh seed Angelique Kerber 6-2, 3-6, 6-1.

Thursday's quarterfinals will pit Halep against the tough left-hander Makarova; Wozniacki versus Pennetta; Safarova against Pliskova; and Suarez Navarro versus Muguruza.

The 2015 Dubai champion will claim $456,000.