Serena Williams beat Maria Sharapova for the 15th straight time yesterday, rallying in both sets to win 6-4, 6-3 at the Sony Open semifinals in Key Biscayne, Fla.Williams, seeking a record seventh Key Biscayne title, improved to 16-2 against Sharapova and hasn’t lost to her since 2004.The No. 1-ranked Williams won with a better returns and superior serve and. She hit nine aces and broke five times, which helped her rebound from deficits of 4-1 in the first set and 2-0 in the second.”I wasn’t playing my best,” Williams said