Top-seeded Becker defaults in Tiburon

   Top-seeded Benjamin Becker defaulted from his second-round match against Jack Sock on Thursday in the $100,000 First Republic Bank Tiburon (Calif.) Challenger.
   Becker had aggravated a torn groin muscle suffered four weeks ago while playing for Germany in a Davis Cup doubles match. He lost in the first round of last week's $100,000 RelyAid Natomas Challenger in Sacramento to Daniel Kosakowski, a 20-year-old wild card, but said he had no pain.
   Meanwhile, second-seeded James Blake suffered a blow in his quest to pull off a Sacramento-Tiburon double, which 6-foot-10 Ivo Karlovic accomplished last year. Blake's scheduled second-round match against Kosakowski at the Tiburon Peninsula Club was postponed by rain until today at 11 a.m. The winner will play Mischa Zverev, a Moscow native who plays for Germany, at 4 p.m. or later.
   Surviving both matches in one day against two players who reached the semifinals or better last week would be difficult for Blake, the oldest player in the singles draw at almost 33. Blake edged the 25-year-old Zverev 6-1, 1-6, 6-4 in the Sacramento final.
   Becker and Blake are the only top-100 players in the singles draw at No. 84 and No. 87, respectively.
   The Blake-Kosakowski winner will give the United States seven of the eight quarterfinalists. Sock (20 years old) will face Rhyne Williams (21) in a matchup of unseeded players at 11 a.m., followed by eighth-seeded Bobby Reynolds (30) against wild card Bradley Klahn (22). Seventh-seeded Denis Kudla (20) will meet unseeded Johnson (22) after the Blake-Kosakowski match.     
   Kudla qualified for the SAP Open on the ATP World Tour in San Jose, 64 miles south of Tiburon at the other end of the San Francisco Bay Area, in February and extended No. 2 seed Andy Roddick to 6-7 (5), 7-6 (5), 6-4 in the second round. Roddick twisted his right ankle late in the second set.
   Karlovic is back on the ATP World Tour after his ranking dropped last year because of Achilles' tendon-related surgery.