Mardy Fish booked his first ATP quarter-final in five months as the top seed progressed at the ATP/WTA Washington event with a 6-3, 6-1 win over Ricardas Berankis.
Fish, who missed two months of the season with an accelerated heartbeat problem, will face unseeded Belgian Xavier Malisse after the 32-year-old beat French sixth seed Jeremy Chardy 6-3, 6-2.
Malisse and Fish, ranked 15th in the world after breaching the ATP top 10 last season, are 2-2 but have not played in six years.
Fish on Thursday crushed Berankis, who moved up 38 spots in the world rankings to 103 after reaching last week's Los Angeles final.
Fish said that the ankle which forced him to withdraw two weeks ago from Atlanta is not bothering him.
"It feels fine, it's not perfect but I can handle it. Things are getting better. I'm pleased with how I'm playing, it was good to win in an hour and try to get ready for the quarter-final tomorrow."
Fish, who ruled himself out of the London Games, hammered down 10 aces against Berankis, breaking four times in his rout.
South African Kevin Anderson seeded third, beat Florent Serra of France 6-4, 6-4.
Anderson earned his third hardcourt win of the summer after reaching the second round in Atlanta.
He punished qualifier Serra with 12 aces in a match lasting just under 90 minutes, with Anderson breaking three times and losing only one serve.
Anderson will next play number eight Sam Querrey, another big hitter who has been steadily raising his ranking this season after two years of injury. The Californian fired nine aces to the eight of Germany's Benjamin Becker in a 6-4, 6-3 result.
Querrey leads Anderson by a narrow 5-3 margin, with the South African winning their last two meetings this season in Miami and Houston. The pair will play for the fourth time in 2012.
In women's quarter-final play, Russian top seed Anastasia Pavlyuchenkova advanced over Chang Kai-chen of Taiwan 6-4, 6-4. Chang saved seven of the 10 break points she faced.
Third seed Sloane Stephens of the US beat Wimbledon junior winner Eugenie Bouchard, of Canada, 6-4, 6-4.
Fourth seed Vania King won an all-American clash over seventh seeded Californian Coco Vandeweghe 6-1, 3-6, 6-4, after staring with a 5-0 lead.
Magdalena Rybarikova of Slovakia advanced over compatriot Jana Cepelova 6-2, 6-4.