Williams is usually seeded higher in the ranks, but two years of illness and injuries have contributed to her lower rank. Technically, she pulled off the upset Monday by defeated Wimbledon semifinalist Kirsten Flipkens 6-1, 6-2.
The seven-time major champ faced Flipkens a few weeks back in a similar situation, winning the first set in Toronto 6-0. Flipkens came back though, to win the match in three sets.
Williams will face the winner of Kiki Bertens and Jie Zheng in the second round.