The 29-year-old Williams - who struggled on Saturday in her first round win over another Russian, Vera Dushevina - clawed her way through the first set despite erratic play, closing it out with a blistering forehand down the line.

But Pavlyuchenkova, ranked 39 in the world, remained undaunted, breaking Williams - who had 14 double faults - to go up 3-1 in the second set and cruising to force the third-set decider.

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She again broke Williams in the first game of the third set and dictated play for much of the set, with the seven-time Grand Slam winner failing to find her range, spraying ground strokes both into the net and beyond the baseline.

The Russian, serving for the match at 5-2, battled her nerves, double faulting to lose the game at love. Williams held her serve, but Pavlyuchenkova steadied herself to close out the victory with a forehand winner.