Second-seeded Chanelle Scheepers and No. 5 Barbora Zahlavova were both first-round losers at the $220,000 Citi Open tennis event on Monday.
Slovakian Magdalena Rybarikova, 23, cruised past the 42nd ranked player in the world, Scheepers, 6-2, 6-1 on the hardcourts at the William H.G. FitzGerald Tennis Center.
Rybarikova won 5-of-9 break points and fired five aces against the South African, who committed five double faults.
Hungarian Edina Gallovits-Hall upset the Czech Zahlavova 7-5, 4-6, 6-3.
In other seeded action Monday, No. 3 American Sloane Stephens downed Sesil Karatantcheva of Kazakhstan 6-3, 2-6, 6-1, seventh-seeded American Coco Vandeweghe was a 6-4, 6-1 winner of Japan's Erika Sema and eighth-seeded Belarusian Olga Govortsova drilled Czech Karolina Pliskova 6-2, 6-2.
Additional opening-round wins came from Swede Johanna Larsson, Slovak Jana Cepelova, Greek Eleni Daniilidou, Hungarian Melinda Czink, American Irina Falconi and France's Aravane Rezai.
This week's top seed is Russian Anastasia Pavlyuchenkova.
The 2012 D.C. champion will collect $37,000.