Defending champion Venus Williams is out of the Dubai Tennis Championships after losing in the third round in straight sets to 11th-seeded Lucie Safarova.

The eighth-seeded Williams looked listless in the humid 93 degree Fahrenheit (34 c) temperatures as Safarova cruised to a 6-4, 6-2 victory.

Williams offered Safarova six opportunities to break serve and the Czech player took advantage four times, twice in each set.

Joining Williams on the sidelines was fifth-seeded Agnieszka Radwanska, who lost 6-4 6-2 to unseeded Garbine Muguruza of Spain.

Sixth-seeded Ekaterina Makarova of Russia reached the quarterfinals by beating Zarina Dyas of Kazakhstan 6-3, 6-4.