Williams and Azarenka, both former world No. 1s, are working their way back to high level tennis following injuries and illness. After the 10th-ranked Azarenka, who celebrated her 25th birthday, saved three match points to tie it 6-6, Williams won the first five points in the tiebreaker. Azarenka's second serve was the biggest difference between the hard-hitting players. Williams, in her 12th career appearance at Stanford, reached her 10th quarterfinal. Fifth-seeded Ana Ivanovic also advanced, beating qualifier Carol Zhao 6-1, 6-1. After the match today I went back out on the court to get the rhythm back on my serve. Zhao, a sophomore All-America at Stanford, appeared in her second WTA Tour event and gained her first career win at the level Tuesday when Yanina Wickmeyer retired because of a viral infection.