NEW YORK (AP) -- Former champion Samantha Stosur is out at the U.S. Open.

The 24th-seeded Australian lost to Kaia Kanepi 3-6, 6-3, 7-6 (8) in the second round Thursday.

Stosur, who won the 2011 U.S. Open title, holds the distinction as the last woman to beat Serena Williams at Flushing Meadows. Williams has won the past two titles and on Thursday extended her winning streak at the tournament to 16 matches with a 6-1, 6-0 victory over Vania King.