Sock reaches another milestone

   Jack Sock reached another milestone Sunday in his promising career.
   The 20-year-old American won his first Challenger title, edging Mischa Zverev of Germany 6-1, 1-6, 7-6 (3) in the $100,000 First Republic Bank Tiburon (Calif.) Challenger at the Tiburon Peninsula Club. Both players were unseeded.
   Sock, from Lincoln., Neb., won U.S. Open titles in 2010 (boys singles) and last year (mixed doubles with Melanie Oudin).
   Sunday's score was almost identical to James Blake's 6-1, 1-6, 6-4 victory over Zverev, 25, in the final of the previous week's $100,000 RelyAid Natomas Challenger in Sacramento.
   Sock jumped 55 places in the world rankings to a career-high No. 165 and earned $14,400 for the title. Zverev improved 13 spots to No. 140 and pocketed $8,480.
   Fourth-seeded Rik de Voest and Chris Guccione won the doubles title, beating second-seeded Jordan Kerr and Andreas Siljestrom 6-1, 6-4 in a matchup of similar teams.
   De Voest and Kerr are 32. Guccione and Kerr are Australian. Guccione is 6-foot-7 and Siljestrom 6-9. Guccione, however, is the only left-hander. He won last year's crown with Carsten Ball.