Anke Huber took her place in the final eight after French Open champion Mary Pierce was forced to retire through a shoulder injury.

Pierce had lost the first set 6-4 and had double faulted six times during the 38 minutes of play.

Huber, the 10th seed from Germany, will now face Russia's Elena Dementieva in the quarter finals who defeated American Lilia Osterloh.

"The day before yesterday, after my match with Lisa Raymond, I was 100 percent," said Pierce.

"In doubles it got sore and it was sore today. Every serve I hit it got worse."

Pierce won the French Open in June but has played just two matches in between the two tournaments, both at Wimbledon.

Spotted

Her opponent spotted her injury from the beginning of the match.

"I saw it right in the first service game," Huber said. "It's hard to play when you see her not 100 percent."

Reigning US Open champion Serena Williams overcame a first half scare to power her way to a 7-6 6-0 victory over Jelena Dokic in the fourth round.