Anastasia Rodionova has joined countrywoman and ninth seed Daria Gavrilova in the third round of the Charleston Open.

Rodionova was too strong for 2012 French Open finalist Sara Errani, disposing of the Italian in straight sets 6-2 6-2.

Gavrilova, the ninth seed in South Carolina, won 6-3 6-1 over Alison Riske of the US .

Laura Siegemund of Germany beat Venus Williams 6-4 6-7 (7-3) 7-5 on Wednesday to win her second three-set match in three days and move on to the third round at the Volvo Car Open.

Elsewhere, Russian Daria Kasatkina outlasted Puerto Rican Olympic champion Monica Puig 6-0 6-7 (7-3) 6-2.

Kasatkina, who came close to making the semifinals here last year, hit 19 winners with 18 unforced errors to finally escape after just over 2 hours on court. Puig hit more winners (25) but also had 41 errors, including on match point.

The former French Open junior champion will face good friend and doubles partner Gavrilova.

Teenage qualifier Fanny Stollar caused a major upset with a 7-6 (9-7) 7-6 (7-3) win over fourth seed Elena Vesnina.

The 18-year-old Hungarian was twice a break behind in the opening set but Vesnina could not make the most of all the break points she had as Stollar responded with 13 aces to keep herself in the match.

She edged ahead in the tie break and assumed control, leading for most of the match, but appeared unable to get over the line as Vesnina, a two-time Charleston finalist, saved five match points at 5-4 in the second set to force another tie break.

However, Stollar prevailed once more and took victory in two hours and five minutes to set up a clash with fellow youngster Jelena Ostapenko, after the Latvian took out top ranked Greek star Maria Sakkari 6-2 4-6 6-2.

There were also straight sets victories for Naomi Osaka, Kiki Bertens, Mirjana Lucic-Baroni, Ons Jabeur and Anastasija Sevastova.