The top-seeded Kerber, the defending champion, advanced to the quarterfinals with a 6-2, 6-3 victory over Slovakia's Kristina Kucova. Williams looked like she would join the reigning
Kerber will face
No. 7 seed
The last match Friday pits Russian qualifier
Kerber needed a third-set tiebreaker to move on in her first match on Tuesday night, saying many of her errors came from making the transition from hard courts to the first clay event of the season. Kerber seemed to adjust quickly this time out against Kucova.
Kerber continued to gain confidence in the season's first clay-court tournament. She needed a third-set tiebreaker to win her opening match on Tuesday night. This time, Kerber relied on her steady groundstrokes and relentless returns to knock off Kucova.
Kerber broke her opponents' serve seven times and said she began to the feel the excitement here she did a year ago when she captured the title.
"I think the feeling is coming back like I had last year because right now, I'm feeling much better on clay again," she said.
Williams also overcame some issues after dropping a first-set tiebreaker and rallying to move in front of Putintseva, who was 0-3 all-time against the U.S. great.
The 21-year-old Putintseva, though, dug in to pull off the upset.
Putintseva fought through five deuces — three of them with Williams a point away from going up 3-1 — to tie the third set and then run out to a 4-2 lead. After Williams rallied back a final time and the large, stadium court crowd cheering her on, Putintseva bore down to close out the victory and beat a second former Volvo champion in as many matches. Putintseva defeated 2009 winner
Putintseva jumped around after the victory, pumping her fists and celebrating. Ranked 61st in the world, she entered the match with a 3-14 record all-time against players in the top 20.
Williams' steady serve unraveled down the stretch: She made seven of her 11 double faults in the third set.
Sock advances to quarterfinals
Defending champion Jack Sock beat Australia's Matthew Barton, 6-2, 7-6 (5) on Thursday to reach the quarterfinals in the U.S. Men's Clay Court Championship.
The fourth-seeded American won last year at River Oaks for his first ATP Tour title. He will face seventh-seeded