Andy Roddick [ Images ] stayed on course for a fifth Queen's Club title on Thursday when fellow American Mardy Fish [ Images ] retired after one set of their Centre Court clash.

Third seed Roddick showed plenty of venom in his serve to edge the opening set 7-6 before a tight contest was curtailed by an ankle injury to Fish.

"Hopefully it's only a two or three day thing and he'll be ready for Wimbledon [ Images ]," a sympathetic Roddick said after extending his winning record over his close friend to 9-1.

"The level of tennis in that set was very high, so I'm happy with that. I've not being serving much lately and it takes a while to get that snap back," added Roddick, who missed the French Open [ Images ] with an injury to his serving shoulder.

Holder Roddick will meet the winner of Briton Andy Murray [ Images ] and Latvian Ernests Gulbis [ Images ] in the last eight.

Eighth seed Ivo Karlovic [ Images ] sent down 10 aces against Chile's Fernando Gonzales as the giant Croat reached the quarter-finals with a 6-3, 7-5 victory.

Later on Thursday four-times French Open champion Rafael Nadal [ Images ], the top seed here, takes on Japan's [ Images ] Kei Nishikori while second seed Novak Djokovic [ Images ] meets fellow Serb Janko Tipsarevic [ Images ].

Australian Lleyton Hewitt [ Images ], another four-times winner of the Wimbledon warm-up tournament, plays Frenchman Paul-Henri Mathieu.