Andy Roddick stayed on course for a fifth Queen's Club title on Thursday when fellow American Mardy Fish 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," 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 with an injury to his serving shoulder.
Holder Roddick will meet the winner of Briton Andy Murray and Latvian Ernests Gulbis in the last eight.
Eighth seed Ivo Karlovic 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, the top seed here, takes on Japan's Kei Nishikori while second seed Novak Djokovic meets fellow Serb Janko Tipsarevic.
Australian Lleyton Hewitt, another four-times winner of the Wimbledon warm-up tournament, plays Frenchman Paul-Henri Mathieu.
