Peng will play Saturday against fourth-seeded Sabina Lisicki of Germany, who also overcame a one-set deficit to eliminate Urszula Radwanska of Poland 3-6, 7-5, 7-6 (4).
Third-seeded Sorana Cirstea of Romania ousted Michelle Larcher de Brito of Portugal 6-2, 7-6 (5), while fifth-seeded Magdalena Rybarikova of Slovakia routed Ioana Raluca Olaru of Romania 6-1, 6-2.
All four players are looking for their first WTA Tour title.
The 40th-ranked Peng reached the third round of Wimbledon and was runner-up at the Forest Hills Classic in August and at Guangzhou last week.
Cirstea, ranked 46th, hasn't dropped a set on the way to her first semifinal this season. She was a runner-up in Budapest last year.
The 19-year-old Lisicki reached the Australian Open third round and played in her first quarterfinal at Cincinnati in August.
Rybarikova, who will turn 20 on Saturday, advanced to the third round of the U.S. Open in September. The 65th-ranked Slovak will be playing her first WTA Tour semifinal.
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