Top seed and defending champion Angelique Kerber had few issues as she eased into the semi-finals of the WTA event in the US city of Charleston.
Irina-Camelia Begu made 35 unforced errors as she went down 6-2 6-3 to the Australian Open champion in 72 minutes.
“I think I was mentally there. I was trying to focus on myself because it’s always tough to play against her,” Kerber said.
“Sometimes you lose your rhythm against her, so that’s what I was focusing on: 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.
“I’m feeling better and better on clay. I think I’m getting used to it and it’s just so great to be back in the semis.”
Kerber will face American Sloane Stephens in the last four after the American beat Daria Kasatkina 6-1 5-7 7-5.
Stephens raced through the opening set but a late break in the second enabled the Russian to tie the match.
Stephens faced a match point in the deciding set but reeled off 11 straight points to take victory and advance.
Elena Vesnina continued her resurgence with a 7-5 6-4 victory over Laura Siegemund and she will face Sara Errani after her 7-6 (7-2) 6-1 win over Yulia Putintseva.