Carlsbad - Former US Open champion Samantha Stosur and Virginie Razzano notched upset victories on Friday to set up a semi-final clash at the WTA Tour's Southern California Open.
Fifth-seeded Australian Stosur ousted second-seeded Agnieszka Radwanska of Poland 7-5, 2-6, 6-3.
French wild card Razzano continued her remarkable run at the $795,707 US Open tuneup with a 6-7 (6/8), 7-5, 7-6 (10/8) triumph over third-seeded Czech Petra Kvitova.
Razzano, who has also beaten two-time Grand Slam champion Svetlana Kuznetsova and eighth-seeded Spaniard Carla Suarez Navarro this week, saved two match points in the third-set tiebreaker en route to the victory.
The three-hour, 35-minute match was the second-longest on the WTA Tour this year, behind Bethanie Mattek-Sands' three-hour, 42-minute victory over Anastasia Rodionova on the clay courts of Charleston in April.
Razzano took a 5-3 lead in the third set, but let three match points slip away.
Kvitova, a former Wimbledon champion, served for the match at 6-5, but Razzano broke her to force the decisive tiebreaker.
Kvitova rolled to a 5-2 lead, but Razzano rallied and sealed it on her fifth match point.
"I think I was nervous," Razzano said.
"I am human. You know you are not too far from the win and you must take your emotions out of it.
"I tried to stay positive and never imagine I could lose."
Stosur recovered from an early break in the third set to down 2011 Carlsbad winner Radwanska and reach her first semi-final of the season.
"I'm obviously very happy with today's win," Stosur said.
"To come to a tournament where you weren't expecting to play and decide at the last minute after being given a wild card, it's fantastic to have really made the most of that opportunity and now be in the semis."
Top-seeded Victoria Azarenka of Belarus completed a bad day for the Radwanska family when she ousted Agnieszka's unseeded sister, Urszula, 6-1, 6-2.
Azarenka next faces seventh-seeded Ana Ivanovic of Serbia who beat fourth-seeded Roberta Vinci 6-1, 6-7 (1/7), 6-2.
In doubles, number three seeds Raquel Kops-Jones and Abigail Spears rallied from a 6-4, 3-0 deficit to beat Daniela Hantuchova and Martina Hingis 4-6, 7-5 10/3.
Their victory ended Swiss great Hingis' first tournament since returning to action after six years away from the game.
Hingis, now 32, won five Grand Slam singles titles and nine in doubles and was ranked number one in the world for a total of 209 weeks before she retired for the first time at the age of 22 in 2003.
She launched a comeback in 2005 only to retire again in November of 2007, but says her experience playing World Team Tennis inspired her to attempt a comeback to the WTA that so far she plans to limit to doubles.
Results from the fifth day of the $795,000 WTA Southern California Open (x denotes seed):
Virginie Razzano (FRA) bt Petra Kvitova (CZE x3) 6-7 (6/8), 7-5, 7-6 (10/8)
Ana Ivanovic (SRB x7) bt Roberta Vinci (ITA x4) 6-1, 6-7 (1/7), 6-2
Samantha Stosur (AUS x5) bt Agnieszka Radwanska (POL x2) 7-5, 2-6, 6-3
Victoria Azarenka (BLR x1) bt Urszula Radwanska (POL) 6-1, 6-2