Williams, seven-time Grand Slam singles winner, built a 3-0 lead early in the second set, but resilient Wang made her comeback into contention collecting three games in a row.

Wang surrendered her leads in both sets when facing Williams at the same phase last year, but the 91st-ranked Chinese refused to let her chance slip away this time. After the two players shared the next four games for a 5-5 tie, Wang broke Williams' service and recorded her stunning victory over William.

Williams suffered disastrous 35 unforced errors despite notching 28 winners, also inferior to Wang in terms of points on first and second serves.

Wang will next face Croatia's Petra Martic, who eliminated Wang's compatriot Wang Yafan in an earlier match-up.