Robredo, the third seed, beat Russian Teimuraz Gabashvili 6-4, 6-0 to advance to a semifinal match Saturday against Juan Monaco. Monaco held a 6-1, 3-1 lead over ninth-seeded Fernando Verdasco when Verdasco retired due to a right calf injury.
"In the first game of the match, I pulled a muscle in my calf," Verdasco said in a statement on the men's tennis Web site. "It was really hard to play after that. I had real pain when serving."
Second-seeded Robin Soderling of Sweden, a fan favorite and surprise French Open runner-up, beat fifth-seeded Nicolas Almagro of Spain 7-5, 6-3 and Swede Andreas Vinciguerra topped Austrian Jurgen Melzer 2-6, 6-4, 6-3.