Washington - Wimbledon semi-finalist Milos Raonic reached the quarter-finals of the ATP and WTA Washington Open with a 7-6 (7/1), 7-6 (7/3) victory on Thursday over Australian Lleyton Hewitt.
The second-seeded Canadian fired 27 aces and denied all four of the two-time Grand Slam champion's break chances at the $1.9 million (1.4m euro) hardcourt warm-up event for the US Open.
"I did a lot of good things, especially the way I fought through the important games," Raonic said. "In those key moments, my attitude got me through."
Raonic, who also won his opener over American Jack Sock in two tie-breakers, will face US giant-killer Steve Johnson for a spot in the last four.
Johnson dumped ATP aces leader Ivo Karlovic 3-6, 7-6 (7/4), 7-6 (9/7) despite 27 aces by the Croatian ninth seed a day after beating US fifth seed John Isner, who ranks second in aces and fired 29 past Johnson.
"He couldn't have had any better preparation to face me," said Raonic, who ranks third in ATP aces. "It's going to be very difficult.
"Compared to the previous two he got, I think I control the center of the court and move a little better. Hopefully that will get me through."
In each win, Johnson benefitted from a double fault by his rival on the penultimate point to win a third-set tie-breaker.
"They're getting shorter every day, which is good," Johnson said of his big-serving opponents. "I can learn a lot from a match like this and take it into the next match."
And Johnson could face South African seventh seed Kevin Anderson, who ranks sixth on the season aces list, in the semi-finals.
Anderson downed Tunisia's Malek Jaziri 6-3, 6-4 to reach a quarter-final match with American left-hander Donald Young, who outlasted Uzbek Denis Istomin 6-3, 3-6, 6-3.
Young, ranked 73rd, has won three ATP main draw matches in a row for the first time since a run to his only ATP final in 2011 at Bangkok, where he lost to Britain's Andy Murray.
"I'm excited about it," Young said. "I had to fight some nerves. I'm happy to get through. It's a big win for me."
French sixth seed Richard Gasquet, coming off a right arm injury that saw him withdraw last week at Atlanta, beat American Tim Smyczek 6-3, 6-2.
"I couldn't even serve a ball," Gasquet said. "For three days I didn't serve. Now I'm very sound. I feel no pain. It feels fine."
Russians Ekaterina Makarova and Anastasia Pavlyuchenkova, the two top seeds remaining in the women's draw, booked a quarter-final meeting with straight-set triumphs.
Second seed Makarova beat American Lauren Davis 6-2, 6-4 and fifth-seeded Pavlyuchenkova defeated Japanese qualifier Hiroko Kuwata 6-3, 6-3.
Russian sixth seed Svetlana Kuznetsova, the 2004 US Open and 2009 French Open champion, ousted Belgium's Kirsten Flipkens 6-4, 7-5 to book a last-eight date with Vania King, a 6-1, 6-3 winner over fellow American Christina McHale.
Results on Thursday from the fourth day of the $1.9 million (1.4m euros) Washington Open (x denotes seed):
Kevin Anderson (RSA x7) bt Malek Jaziri (TUN) 6-3, 6-4
Steve Johnson (USA) bt Ivo Karlovic (CRO x9) 3-6, 7-6 (7/4), 7-6 (9/7)
Donald Young (USA) bt Denis Istomin (UZB) 6-3, 3-6, 6-3
Milos Raonic (CAN x2) bt Lleyton Hewitt (AUS) 7-6 (7/1), 7-6 (7/3)
Richard Gasquet (FRA x6) bt Tim Smyczek (USA) 6-3, 6-2
Vasek Pospisil (CAN) bt Tomas Berdych (CZE x1) 6-2, 6-4
Santiago Giraldo (USA) bt Victor Estrella Burgos (DOM) 6-2, 6-0
Kei Nishikori (JPN x4) bt Lukas Lacko (SVK) 6-2, 2-6, 6-3
Svetlana Kuznetsova (RUS x6) bt Kirsten Flipkens (BEL) 6-4, 7-5
Anastasia Pavlyuchenkova (RUS x5) bt Hiroko Kuwata (JPN) 6-3, 6-3
Vania King (USA) bt Christina McHale (USA) 6-1, 6-3
Ekaterina Makarova (RUS x2) bt Lauren Davis (USA) 6-2, 6-4