Vania King and Coco Vandeweghe won Wednesday at the Citi Open to set up an all-American quarterfinal.
The fourth-seeded King beat Irina Falconi 6-2, 7-6 (5), and No. 7-seeded Vandeweghe topped qualifier Aravane Rezai 6-2, 6-2. A third American, third-seeded Sloane Stephens, already advanced to the quarterfinals Tuesday.
Top-seeded Anastasia Pavlyuchenkova avoided an upset with a 6-2, 2-6, 6-3 victory over Melinda Czink.
King was up 6-5 in the second set and had a chance to win with Falconi serving, but hit a shot wide on match point, then again on the next point and Falconi pulled out the game.
''I wasn't calm enough. Obviously I was nervous,'' King said. ''I kind of second-guessed myself.''
On the final match point in the tiebreaker, Falconi hit a shot wide to give King the victory.
''I know every match I win will boost my confidence and help my game,'' King said. ''I feel like my game is there, I just need to play more matches and get used to the competition.''
Four seeded players have already been knocked out of the women's draw. The latest to go was eighth-seeded Olga Govortsova, who was beaten by 18-year-old Eugenie Bouchard 1-6, 6-0, 6-3. The win put Bouchard in her first career WTA Tour quarterfinal.
Qualifier Jana Cepelova also advanced to her first quarterfinal, beating Edina Gallovits-Hall 6-3, 6-4, and Magdalena Rybarikova topped Eleni Danilidou 6-3, 7-5.
On the men's side, Second-seeded Alexandr Dolgopolov beat Rueben Ramirez Hidalgo 6-1, 6-3, and James Blake advanced with a 6-2, 6-4 victory over qualifier Marco Chiudinelli.
''Anytime you do that, it's a pretty darn good feeling,'' Blake said. ''Right from start to finish I felt good.''
Fourth-seeded Tommy Haas beat Leonard Mayer 6-4, 7-5 to set up a quarterfinal with fellow German Tobias Kamke. Kamke beat Marinko Matosevic 6-4, 6-3.
''I'm pretty pleased with the way I played the big points and the position I put myself into,'' Haas said.
It will be the first time Haas and Kamke have played each other.
''It should be quite interesting,'' Haas said. ''It's always tough when you play someone for the first time, to figure out how they play or what they do like and what they don't like, but I look forward to it.''