The American seventh seed lost the first two games of the match before finding her range, sending her French opponent ranked 61st in the world scampering around Centre Court with a barrage of powerful groundstrokes.

The 29-year-old Williams, playing only her third match since returning to action following serious injury and health problems, struggled for rhythm in the second set and Rezai took full advantage.

But Williams, bidding for her third Wimbledon title in a row and fifth overall, regrouped to make an early break in the deciding set and book her place in the second round.