CHARLESTON, South Carolina (REUTERS) - Australian Open champion Angelique Kerber eased past nemesis Irina-Camelia Begu with a 6-2 6-3 victory on Friday that put her into the semi-finals of the Volvo Car Open clay court event in South Carolina.

Defending champion Kerber will next face seventh-seeded American Sloane Stephens, who battled past 18-year-old Russian Daria Kasatkina, the 14th seed, 6-1 5-7 7-5 in two hours 24 minutes.

The top-seeded German had lost two of three encounters with the big-hitting Begu last year and was 2-2 overall against the Romanian in career head-to-head meetings.

"I was trying to focus on myself because it's always tough to play against her. Sometimes you lose your rhythm against her, so that's what I was focusing on," Kerber said in an on-court interview.

"Just trying to go for it, move good on clay and just win the match because I remember the last match against her, I lost!" added the German, who fell to Begu on clay in Rome after losing to her at the 2015 Australian Open.

Begu did not appear to be at her best following a difficult Round of 16 clash against Monica Puig which was decided by a third set tie-break under the lights on Thursday.

The Romanian was loose with her groundstrokes, amassing 35 unforced errors to only nine by Kerber, who did not face a single break point in the 72-minute match.

Later quarter-finals have fifth-seeded Italian Sara Errani facing Yulia Putintseva of Kazakhstan, and Laura Siegemund of Germany taking on Russian Elena Vesnina.