WASHINGTON, April 13 (Xinhua) -- Australian Open runner-up Marcos Baghdatis of Cyprus retired from a second round match as his rival American Vince Spadea made it through to the quarterfinals at the ATP Houston international on Thursday.

    The surprise Australian Open runner-up complained about the soreness in his lower back while he was trailing behind 6-2, 3-1. He then quit from the match.

    "I don't really know what it is yet. Maybe the nerve is squeezed, I just felt pain coming down through my leg," said the fourth seed.

    "Maybe fatigue has something to do with it. Since Australia I've been playing all the time."

    Spadea, who has 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 theyear.

    The 31-year-old veteran next plays fellow American Mardy Fish, who went through when Germany's Rainer Schuettler handed him a walkover.

    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.

    The remaining two quarterfinals are Austrian Jurgen Melzer versus Fernando Vicente from Spain and blockbuster confrontation between defending champion Andy Roddick and Germany's Tommy Haas. Enditem