Los Angeles - Australian Open champion Angelique Kerber cruised into the WTA claycourt semi-finals in Charleston on Friday with a 6-2, 6-3 victory over Irina-Camelia Begu.
The top seed from Germany had lost two of her prior three meetings with Begu, but the Romanian looked tired after saving a match point in her third-round win over Monica Puig on Thursday.
"I think I was mentally there. I was trying to focus on myself because it's always tough to play against her," said Kerber, who must beat seventh-seeded American Sloane Stephens in the semis to retain the world number-two ranking.
"Sometimes you lose your rhythm against her (Begu) 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."
Begu produced 23 winners in the second set, but her 35 unforced errors doomed her bid to mount a rally.
"I'm feeling better and better on clay," Kerber said.
Stephens defeated 14th-seeded Russian Daria Kasatkina 6-1, 5-7, 7-5.
Stephens said she had expected a tough match even though the Russian was playing in her first Premier-level quarter-final on clay.
"She's had some really good results, so I knew from the beginning that it was going to be a battle," she said.
"The wind and we're on clay court, (there) were a lot of factors, so I'm happy I stayed calm and played my game."
Russian qualifier Elena Vesnina, who toppled second-seeded Belinda Bencic in the second round, reached the semi-finals with a 7-5, 6-4 victory over Germany's Laura Siegemund.
Vesnina, a Charleston finalist in 2011 who has been ranked as high as 21st in the world, also struggled with the wind, and after racing to a 4-1 lead saw Siegemund battle back to 5-5 in the first set.
Vesnina broke once more to pocket the opening set, and was able to make an early break in the second to reach a meeting with fifth-seeded Italian Sara Errani -- a 7-6 (7/2), 6-1 winner over Kazakhstan's Yulia Putintseva.