Tommy Haas continued the run of form which has taken him from outside the top 200 to world No. 36 as he beat Argentina's Leonardo Mayer 6-4, 7-5 at the ATP/WTA event in Washington. The 34-year-old German fourth seed is playing some of the best tennis of his career after finally regaining full potential following a hip operation last year. He is playing for keeps this week in the US capital as he tries to bury the disappointment of missing the London Olympics. The German federation refused to nominate him for wild card tournament consideration. Haas on Wednesday lined up a quarter-final clash with compatriot Tobias Kamke, who earned a revenge win over Marinko Matosevic, 6-4, 6-3. The Australian had beaten Kamke last week in Los Angeles. Haas, who defeated Roger Federer to win at Halle in June, improved his 2012 record to 21-9 as he bids for a 14th career trophy. He advanced over Mayer in just over 90 minutes, hammering eight aces including two in the 11th game of the second set. The veteran, who came to Washington for the first time 15 years ago, then broke a game later to clinch the win. "It was a good win, a very hard-fought match," said Haas. "He has a big serve and there was a lot of guessing on my part out there. "We had tough, humid conditions and of course it's hot. But that's the beauty of tennis, you have to deal with it all. "Playing Tobias in an all-German match will be good. I'm expecting a good match." Kamke advanced into the last eight on his third match point against Matosevic. In WTA women's play in the newly combined event, American seventh seed Coco Vandeweghe booked a spot in the quarters by defeating Aravane Rezai of France, 6-2, 6-2. She next plays compatriot Vania King, the fourth-seeded winner over Irina Falconi, 6-2, 7-6 (7/5). "The weather was not as hot for the match today, but I'm very glad to go through. I'm playing well so far," Vandeweghe said. Junior Wimbledon winner Eugenie Bouchard of Canada upset eighth seed Olga Govortsova of Belarus 1-6, 6-0, 6-3, returning to the scene of her first main draw win a year ago. Slovakia's Jana Cepelova beat Edina Gallovits-Hall of Romania 6-3, 6-4 while Magdalena Rybarikova defeated Greek Eleni Daniilidou 6-3, 7-5.