The Russian knocked out the top-ranked American 4-6, 6-2, 6-3 to make way into the quarterfinals.
Criticising the the organisers of the tournament for schedule, Williams said, “I wasn"t moving my fastest but all I could do was try and do the best. I don"t know. I definitely wasn"t at my best."
“This isn"t a player—favourite tournament, just to be honest. None of the players are really gung—ho about playing here," she added.
Williams' defeat came after the Tuesday, May 11 match against Vera Dushevina during which the player looked out-of-form. The match, which lasted 3 hours, 26 minutes, was the longest match of Williams' career.