Venus beats birthday girl Azarenka in Stanford

Stanford, CA ( - American Venus Williams spoiled Victoria Azarenka's 25th birthday Thursday by beating the Belarusian in the second round at the Bank of the West Classic, a U.S. Open Series tennis event.

Williams beat Azarenka, the No. 4 seed, by a 6-4, 7-6 (7-1) score on the hardcourts at Taube Family Tennis Center. The former top-ranked Williams titled here in 2000 and 2002 and is a five-time Stanford runner-up.

Williams improved to 4-0 lifetime against Azarenka, who titled here in 2010.

Next up for Williams is No. 8 seed Andrea Petkovic, who won her second round match on Wednesday.

Third seed Angelique Kerber moved into the quarterfinals with a 7-6 (7-4), 0-6, 6-2 victory over Coco Vandeweghe.

Next up for Kerber is rising 20-year-old Spaniard Garbine Muguruza, who grounded aging Slovakian Daniela Hantuchova 6-4, 6-4 to reach her seventh quarterfinal of the year.

Ana Ivanovic handled Carol Zhao 6-1, 6-1 on Thursday. The fifth-seeded Serb will face Serena Williams on Friday.

The 2014 Stanford champion will claim $120,000.