China's Shuai Peng ended Belgium's Kim Clijsters winning steak on American hardcourts with a 6-4, 6-4 upset in the quarter-finals of the San Diego Classic on Friday.
Peng will face France's Mary Pierce, who earlier beat fifth seed Patty Schnyder 6-4, 6-3.
The No. 46-ranked Peng put on a powerful and riveting performance, putting Clijsters on the defensive throughout.
Even though the Belgian tried to mix up her tactics, she was unable to crack Peng's relentless attack from inside the baseline.
"I'm very happy," said Peng, who also beat world number six Elena Dementieva in the second round. "I was so nervous before I went on court and didn't' think about beating her, just playing my game. I told myself if I got chances to believe in myself."
Clijsters had not lost a match on the U.S. hardcourts since she was beaten by compatriot Justine Henin-Hardenne in the 2003 U.S. Open final, but was unable match Peng on Friday.
She compared Peng to a faster version of the nine-times Grand Slam champion Monica Seles and said it was difficult to read her.
"She's one of the hardest hitters I've played," Clijsters said. "She hits incredibly clean, especially from her backhand side. She played unbelievable.
"She came up with better shots every time, even when I was defending well.
"She has a great future ahead of her. She's the best player I've played in a long time.
"I think she can definitely become top three."
A Japanese player will be in the final after Ai Sugiyama routed 15-year-old Bulgarian Sesil Karatantcheva 6-1, 6-2 and Akiko Morigami defeated 18-year-old Russian Anna Chakvetadze 6-3, 6-4 to progress to a semi-final encounter.
"It's great for Japanese tennis," said Morigami. "Maybe it will inspire more kids (back home) to play."
At the French Open in June, the sixth-seeded Pierce needed 11 match points to beat Schnyder in a long three-set contest.
But in Friday's quarter-final, the Frenchwoman simply overwhelmed her foe, answering nearly all of Schynder's change of tactics with huge blows down the line.
Schnyder fought off three match points with a series of ground-stroke winners that had Pierce grinning in amazement, but on the fourth, Pierce blazed a forehand crosscourt the Swiss could not handle.
