American Vince Spadea reached the quarter-finals of the ATP US Clay Court Championships on Thursday as an ailing Marcos Baghdatis retired from their second-round clash.
Baghdatis, the surprise Australian Open runner-up, was trailing 6-2, 3-1 when he called it quits, complaining of a nerve problem in his lower back.
"I don't really know what it is yet. Maybe the nerve is squeezed," said the fourth seed from Cyprus. "I just felt pain coming down through my leg. Maybe fatigue has something to do with it. Since Australia I've been playing all the time, working hard. I haven't wanted to stop." Spadea, who had failed to progress beyond the second round in his past four tournaments since back-to-back semi-final appearances in Delray Beach and San Jose, improved to 11-9 for the year.
The 31-year-old veteran next plays fellow American Mardy Fish, who advanced when Germany's Rainer Schuettler handed him a walkover.
Schuettler was battling a gastrointestinal problem that prevented him from playing.
"I didn't expect to get through this way, but I played a solid match," he said. "I hope for Marcos' sake it's not too serious. Mardy has a different style of game - not a typical clay courter - so it could be a tricky match. I can't let him dictate too much. It will be a tough match."
Fish, who underwent two wrist surgeries last year, began 2006 with a 1-4 record.
But the 2003 Cincinnati finalist showed great improvement at ATP Masters Series events in Indian Wells and Miami and last week won the Tallahassee Challenger.
American Paul Goldstein, 29, reached his second quarter-final of the year with a 6-4, 6-1 win over countryman Scoville Jenkins. Goldstein next plays gritty Spaniard Albert Montanes, who beat German Tomas Behrend 6-2, 6-3. Austrian Jurgen Melzer advanced to his first quarter-final of the year with a 7-6 (7/2), 6-4 win over Brazilian Marcos Daniel.
Friday's quarter-final line-up will be highlighted by the night's blockbuster confrontation between defending champion Andy Roddick and Germany's Tommy Haas, who both advanced on Wednesday.
Haas defeated Roddick in the 2004 final, while last year Roddick won his third title in his fifth consecutive appearance in the Houston final.