Samantha Stosur has been eliminated in the third round of the WTA event in Charleston, beaten by Italian Sara Errani.

Stosur’s serve again proved problematic and was broken in eight of her 11 service games en route to the 6-4 7-6 (7-5) loss.

The No.10 seed and 2010 Charleston champion won just 23 of 66 points on her own serve and only managed to stay in the second set when she broke Errani twice.

Venus Williams is also out of the tournament after losing to Yulia Putintseva of Kazakhstan 7-6 (7-5) 2-6 6-4.

Williams, seeded third and ranked 14th in the world, had a chance to gain a place in the top 10 had she won this match. Instead, Putintseva won five of the final six games on Thursday (Friday AEST) to advance.

Williams became the fifth of the top eight seeds in Charleston to lose before the quarter-finals.

Top-seeded Angelique Kerber avoided that earlier in the day with a 6-2 6-3 victory over Slovakia’s Kristina Kucova.

Kerber is the defending champion after winning the title in last year’s Family Circle Cup. The second-ranked German star was not at her best, but good enough to put away Kucova. Kerber broke her opponent seven times, including the final game.

Australian Daria Gavrilova will face American Sloane Stephens for a place in the quarter-finals later on Thursday (Friday AEST).