Canada's Milos Raonic and Vasek Pospisil advanced to the quarterfinals of the Citi Open with victories here over 2004 champion Lleyton Hewitt and top seed Tomas Berdych, respectively.

The 24-year-old Pospisil, who suffered through a slump in the first half of the year, reached his fourth quarterfinal of the past several weeks by upsetting the big-hitting Berdych 6-2, 6-4.

The Canadian world No. 36 only lost his serve once during Thursday's match and broke Berdych on four occasions to improve his record against the Czech world No. 5 to 2-0.

Pospisil's 82 percent winning percentage on his first-serve points, compared to 66 percent for Berdych, was one of the keys to the upset.

Next up Friday for the Canadian, who partnered with American Jack Sock to win this year's men's doubles title at Wimbledon, will be Colombia's Santiago Giraldo, a 6-2, 6-0 winner Thursday over Dominican Victor Estrella Burgos.

Prior to Pospisil's surprise victory, Raonic carried the flag for Canada on Thursday by edging Hewitt 7-6 (7-1), 7-6 (7-3).

Raonic's powerful serve was once again the key to his triumph, as his clutch aces in the two tiebreakers - and 27 aces for the contest - gave him a slight edge in a match that did not feature a single service break.

The Canadian world No. 7, the No. 2 seed at the Citi Open, will next square off against American Steve Johnson, who eked out a 3-6, 7-6 (7-4), 7-6 (9-7) victory over another big server, Croatia's Ivo Karlovic.

Friday's other two men's quarterfinals will pit Japan's Kei Nishikori against France's Richard Gasquet and South Africa's Kevin Anderson against American Donald Young.

In the women's singles, 20th-ranked Russian Ekaterina Makarova, the No. 2 seed, advanced to the Washington quarterfinals with a 6-2, 6-4 victory Thursday over American Lauren Davis.

The Citi Open is a tune-up event for the U.S. Open, which gets underway on Aug. 25. EFE