Australian lucky loser Samantha Stosur upset third seed Vera Zvonereva 6-3 6-2 today in the second round of the WTA Bank of the West Classic.
Stosur next faces Canadian qualifier Aleksandra Wozniak, who topped Austria's Sybille Bammer on Thursday 6-4 7-5.
Stosur, placed in the draw when American Lindsay Davenport withdrew due to a knee injury, has been to a pair of semi-finals this season -- including an impressive run at Eastbourne.
The Queenslander also claimed the Wimbledon mixed doubles title with American Bob Bryan earlier this month.
Ranked as high as 27th earlier this year, Stosur's season did not begin until April as she dealt with Lyme disease. The time away has resulted in the 24-year-old dropping to 107th in the rankings.
Stosur beat fellow Australian Anastasia Rodionova in the first round.
Swiss veteran Patty Schnyder continued her impressive march through the early rounds, eliminating Russian Alisa Kleybanova 7-6 (10-8) 6-4.
Schnyder had her best effort here two years ago, when she reached the final before falling to the now-retired Kim Clijsters of Belgium.
The 29-year-old also reached the semi-finals in 2005 and was a quarter-finalist both last season and in 2004.
Standing between the 13th-ranked Schnyder and another trip to the round of eight was unseeded Kleybanova, who was in the midst of her best season to date.
But Schnyder, who won the previous meeting between the two in the first round at Gold Coast at the beginning of the season, battled through a tough first-set tiebreaker en route to victory on Thursday.
With the win, Schnyder booked a quarter-final showdown with top-seeded American Serena Williams, who is 32-4 with three titles this year.
Defending champion Anna Chakvetadze of Russia reached the quarters on Wednesday.
The second seed will take on No.6 Marion Bartoli, who eliminated British qualifier Anne Keothavong 6-3 1-6 7-5.
Bartoli has battled injury and inconsistent play since her run to the Wimbledon final in 2007 and recently lost her status as a top-10 player, dropping to No.15.
The 23-year-old Frenchwoman, who has yet to appear in a final this year, improved to just 14-16 in 2008.
