Sam Querrey finished off Benjamin Becker with his eighth ace of the match, winning 6-4, 6-3 on Thursday to advance to the Citi Open quarterfinals.
The eighth-seeded Querrey, the Farmers Classic winner in Los Angeles on Sunday for his first title of the year, won all 24 of his first-serve points and on 22 of Becker's 33 second serves.
"I thought I returned really well," Querrey said. "Especially on his second serves I was really aggressive, more so than normal, and it paid off,"
Querrey will face third-seeded Kevin Anderson, a 6-4, 6-4 winner over Florent Serra.
Top-seeded Mardy Fish also advanced, beating Ricardas Berankis 6-3, 6-1.
In the women's tournament, top-seeded Anastasia Pavlyuchenkova advanced to semifinals, beating Kai-Chen Chang 6-4, 6-4. Pavlyuchenkova was broken early and fell behind 4-1 before rallying to set up her first semifinal match of the year.
"It wasn't my best match today at all," Pavlyuchenkova said. "She went out there and was playing really well. I kept going, and I kept trying to find my energy. I'm happy I pulled it out."
The Russian reached the quarterfinals of the French Open and U.S. Open in 2011, but struggled for much of this year. She reached the quarterfinals in Bastad, Sweden, in her last event.
"Now there's a huge difference and I feel my game is much better than it was two weeks ago," she said. "Maybe it's just my mentality that I'm much more aggressive here."
Pavlyuchenkova will face fourth-seeded Vania King.
King beat No. 7 Coco Vandeweghe 6-1, 3-6, 6-4. King broke Vandeweghe twice to take the first five games, and finished off the third set by breaking Vandeweghe for the fourth time.
Magdalena Rybarikova advanced with a 6-2, 6-4 victory over qualifier Jana Cepelova.