MELBOURNE, Jan. 19 (Xinhua) -- The unseeded Serena Williams Friday survived a major scare before keeping her Australian Open hopes with an upset third-round win over Russian fifth seed Nadia Petrova.

    The American pulled off one of the most unlikely victories of her career as her rival Petrova served for the match in the secondset before she rallied to a 1-6 7-5 6-3 victory in two hours and five minutes.

    Williams, the former world No. 1, who has dropped to 81st in the rankings following a largely inactive 2006 season, will play either Croatian 11th seed Jelena Jankovic or Victoria Azarenka on Sunday.