Previously red-hot Serena Williams was stunned in Friday's quarterfinal action, while her big sister Venus pressed on into the semifinals at the WTA's $2.168 million Western & Southern Open.
The second-seeded former world No. 1 Serena was ousted by fifth-seeded left- hander Angelique Kerber, 6-4, 6-4. The German pulled off the upset in 76 minutes by breaking the American's powerful serve twice while holding her serve throughout on Day 5.
The rising Kerber now has a remarkable seven wins against top-10 women this year.
Serena was riding a torrid 19-match winning streak since being stunned in the first round at the French Open in June. The 14-time Grand Slam champ was seeking a fourth straight tournament title after posting big wins at Wimbledon, Stanford and the London Olympic Games.
Meanwhile, the wild card Venus upended third-seeded U.S. Open champion Sam Stosur 6-2, 6-7 (2-7), 6-4 on the hardcourts at the Lindner Family Tennis Center. The former No. 1 American advanced in 2 hours, 34 minutes despite piling up nine double faults.
The 32-year-old seven-time Grand Slam singles champion Venus, who's been slowed mightily by an autoimmune disease over the last couple of seasons, will now appear in her first semifinal in almost two years, or since the 2010 U.S. Open.
The third round was completed on Friday when 17th-seeded Russian Anastasia Pavlyuchenkova upset sixth-seeded former top-ranked Danish star Caroline Wozniacki 6-4, 6-4 and ninth-seeded Chinese Li Na leveled Swedish qualifier Johanna Larsson 6-2, 6-2. The two matches were suspended/postponed because of rain on Thursday night.
Li was this past Monday's Montreal runner-up to Czech slugger Petra Kvitova.