Anastasia Pavlyuchenkova continued her solid form at the Citi Open, while fellow Russian Svetlana Kuznetsova withdrew injured.
Anastasia Pavlyuchenkova made it back-to-back tournament quarter-finals, upsetting third seed Belinda Bencic at the Citi Open on Thursday.
After making the Baku Cup semi-finals last week, Pavlyuchenkova made it into the last eight in Washington DC with a 6-2 6-4 victory over Bencic.
Bencic had won their only previous encounter - on clay in Rome - but Pavlyuchenkova was too strong at the WTA International hard-court event, saving both break points she faced in the 72-minute encounter.
Pavlyuchenkova will take on Christina McHale in one of two seed-less quarter-finals, after the American edged out Kazakhstan's Yulia Putintseva 6-2 1-6 7-5 in two hours, 45 minutes.
Top seed Ekaterina Makarova was also tested, eventually seeing off qualifier Naomi Broady 6-4 7-6 (7-2) - withstanding 14 aces from the Briton.
Makarova will play sixth seed Irina-Camelia Begu for a spot in the semis, while Louisa Chirico takes on Sloane Stephens - the latter progressing via a walkover after fourth seed and defending champion Svetlana Kuznetsova withdrew due to a lower left leg injury.
Sam Stosur, the second seed, and Monica Niculescu will do battle in the other quarter-final.