LONDON (AP):

Top seeds Rafael Nadal and Novak Djokovic struggled into the quarter-finals at Queen's Club yesterday, but third seed Andy Roddick eased through when fellow American Mardy Fish withdrew with a left ankle injury after losing the opening set 7-6 (5).

Nadal defeated Kei Nishikori 6-4, 3-6, 6-3, but found it difficult to gain the upper hand against the Japanese teenager. After edging the opening set, Nadal was taken to a third when Nishikori forced a backhand error to break for 5-3 in the second.

"Yeah, tough match," Nadal said. "He played well. I didn't play my best match, but I fight, no? I tried my best all the match. I served well, I think. Was my best shot today. Probably in the third set I start returning a little bit better, no?"

Djokovic rallied to overcome fellow Serb Janko Tipserevic 2-6, 6-1, 6-4 after losing the opening four games.

Two break points

Roddick, the defending champion, faced two break points at 2-2 before holding his serve. Fish held off three break points in the next game, hitting two aces and a forehand winner before holding with his seventh ace.

A single mini-break for 2-0 in the tiebreaker was enough for Roddick to win the set.

Roddick has returned to competition after missing several weeks with a shoulder injury, so the shortened match was appreciated.

Roddick next will play Andy Murray, who survived two injury scares before overcoming Latvia's Ernests Gulbis 5-7, 6-1, 6-4. The sixth-seeded Murray double-faulted to concede his serve at 5-5, and then received treatment to his right thumb after Gulbis served out the first set.

After rallying to win the second set convincingly, Murray slipped and injured his groin during the opening game of the third before going on to break for a 5-4 lead.

Murray's thumb injury was diagnosed as a sprain and he said he was not sure whether he could play today.