Karlovic, 11th seed, next plays top seed and the second in the aces race Andy Roddick who beat the third best server on the circuit Sam Querrey 7-6 (7/4), 6-4 to reach the quarter-finals. In the process of overpowering his countryman, the American became the 36th player in the open era to win 500 matches and only the fourth active player behind Swiss Roger Federer (657), Spaniard Carlos Moya (573) and Lleyton Hewitt (511).

Hewitt's stay in the tournament, however, was cut short by defending champion and Argentine second seed Juan Martin Del Potro 6-4, 3-6, 6-7 (2/7).

Hewitt, who blasted 13 aces, took the first set with an early break, but lost the second as he dropped the seventh game after squandering a 40-15 advantage.

Del Potro, who smashed 18 aces, served for the match at 5-4 but the Australian broke him at love and forced the tie-breaker. The Argentine clinched it, winning the last five points with Hewitt making a couple of unforced errors.

Del Potro's next opponent is fifth-seeded Robert Soderling who beat Frenchman Marc Gicquel, 7-5, 5-7, 6-3.

Tenth seed Tommy Haas of Germany defeated Spaniard Juan Carlos Ferrero 7-5, 2-6, 6-1 in a clash between two former top-10 players and will next meet fourth-seeded Chilean Fernando Gonzalez who beat American Wayne Odesnik 6-2, 6-4.

The other two to make quarter-finals were eighth seed Tomas Berdych of the Czech Republic who beat German Phillip Petzschner 4-6, 6-3, 6-3, and American John Isner who defeated French qualifier Sebastien 6-2, 6-4.