Robredo, the 2001 tournament champion and only remaining seeded player at No. 2, trailed 3-0 in the second set before finding his range against the 30-year-old Austrian.
"At 3-0 I was just trying to come back, and when we received
new balls I started to play more aggressively and it worked,"
said the 25-year-old Robredo.
The Russian Simon, who beat American Andy Roddick in the first
round of the French Open this year, proved to be a tough
opponent who played well from the baseline.
"Even though it was hard to finish it, I played a great
match," the 23-year-old Simon told reporters. "I knew I had to
hit the ball very aggressively because Andreev has one of the
strongest forehands in the world."
"It wasn't my day," said Mayer. "I just played a terrible
match. I didn't move well on the court and my serve was bad."
Acasuso will play his first semifinal of the year against Albert Montanes of Spain, who downed Martin Vassallo Arguello of Argentina 2-6, 6-4, 6-2.
Information from The Associated Press and Reuters was used in this report.