Italy's Flavia Pennetta continued her dominance of an injury-hampered Samantha Stosur with a 6-4, 6-3 victory in the quarter-finals of the San Diego Open on Friday.
Fifth seed Pennetta set up a semi-final with twice Grand Slam champion Svetlana Kuznetsova, who ended the hopes of American teenager Coco Vandeweghe 7-5, 6-2.
Pole Agnieszka Radwanska will meet Slovakia's Daniela Hantuchova in the other semi-final after thrashing Israel's Shahar Peer 6-2, 6-0.
Pennetta has never dropped a set in three meetings to world number five Stosur and ran the Australian around the court while notching up 19 winners.
"If I stay doing the same things against her then it's better for me," said Pennetta, who has played 51 matches this year, more than any other player.
"I played backhands down the line deep and I can return her kick serve really well. I have (a) few shots that make her very nervous all the time."
Stosur complained of a muscle injury in her arm that she said had bothered her since her first match at the Stanford Classic last week and had led to a hospital visit after her loss to the Italian.
"It's like a really strong, heavy ache when it starts and I can't get rid of it until I get off the court," said the Australian, who reached her first Grand Slam final at the French Open in June.
"I can't work out what's going on. It hurts every time when I get on court. If I'm going to go on court I want to play the best I can, and maybe now I can't. It can start to wear you down a little."
Kuznetsova had little to complain about in her victory over 18-year-old qualifier Vandeweghe, coming back from 2-5 down and saving a set point in the first set.
Vandeweghe, who had upset Wimbledon finalist Vera Zvonareva in her previous match, double-faulted to hand the Russian a service break then erred on a backhand to concede the set.
Kuznetsova powered away in the second set, taking the match when her visibly tiring opponent missed another backhand.
"It was a great run," said Vandeweghe, who earned a wild card for next week's tournament in Cincinnati.
"But there's a reason why she's a two-time grand slam champion -- she got on top of my pace and made me play a lot more."
Hantuchova overcame a slow start to defeat Russian Kleybanova 2-6, 6-4, 6-3.