Second-seeded Chanelle Scheepers of South Africa and fifth-seeded Barbora Zahlavova Strycova of the Czech Republic both lost first-round matches at the Citi Open on Monday.
Scheepers, ranked No. 42 in the world, fell 6-2, 6-1 to Slovakia's Magdalena Rybarikova. Zahlavova Strycova was beaten by Romania's Edina Gallovits-Hall, 7-5, 4-6, 6-3.
No. 7 seed Coco Vandeweghe of the United States avoided an upset by defeating Olga Govortsova of Belarus 6-4, 6-1.
The Washington tournament, a staple on the ATP schedule, is combining with the WTA Tour for the first time.