Lin Zhu upset top-seeded Zhang Shuai 7-6 (3), 4-6, 6-1 in a marathon quarterfinal at the Jiangxi Open on Friday night.
Zhang committed 50 unforced errors and eight double faults over the two-and-a-half hour match.
Zhu's only other semifinal appearance on the WTA tour was more than two years ago in Kula Lumpur.
Zhu will take on sixth-seeded Saisai Zheng in the semifinals after she beat Fang Ying Xun 6-3, 6-4.
"I'm very happy right now. It was a very tough match for both of us," Zhu said after the match. "We both played great, and she's a great player. It's very tough to beat her, and I'm so happy I did it today."
Second-seeded Qiang Wang remained on course for her first career WTA title when she beat Fangzhou Liu 6-3, 6-0.
Wang fell 2-0 behind then won 12 of the remaining 13 games. She's into her second WTA semifinal.
Wang will meet Magda Linette of Poland, who survived a tough quarterfinal against 17-year-old Australian Open junior champion En-Shuo Liang of Taiwan 6-3, 4-6, 6-2.
"Maybe she's (Liang) not experienced...but she played great. She came out and played like she belonged here already," Linette said. "I already knew her because I saw she won in Australia, so I was expecting a very tough match and it was."
(With input from agencies)