STANFORD, Calif. — Wimbledon champion Serena Williams has advanced to the quarterfinals of the Premier Bank of the West Classic, beating Hungary's Melinda Czink 6-3, 7-6 (7).

Williams, seeded first and ranked No. 2, has won nine straight matches and 13 of 14 overall. She next plays Austria's Samantha Stosur on Friday.

Williams finished with 10 aces Thursday and brushed past her opponent in the first set. Czink, a left-hander, played a stronger second set in forcing Williams to a tiebreaker in a match that lasted nearly two hours.