Three seeds fell at the Pattaya Open on Friday, leaving Russian Ekaterina Makarova as the only seeded player to reach the semi-finals after a three-set battle with Japan's Kimiko Date-Krumm.
Karolina Pliskova fought off two match points to defeat third seed Sorana Cirstea of Romania 1-6, 7-6 (7/3), 6-0 and reach her first semi-final in 11 months.
Russian fifth seed Elena Vesnina was beaten 5-7, 6-3, 6-3 by Germany's Julia Goerges, and Chinese number eight seed Peng Shuai fell 6-2, 7-5 to Czech Andrea Hlavackova.
Fourth-seeded Makarova ended the run of 43-year old Date-Krumm of Japan by winning their entertaining quarter-final 6-2, 4-6, 6-4.
Pliskova was completely outplayed in the opening set of her match, and although she was able to compete at the same level as her opponent in the second set she still struggled to turn the match around.
After two breaks to begin the set, games went with serve until Cirstea held two match points at 5-4.
Pliskova fought off that threat, and Cirstea saved two break points to hold for 6-5 before Pliskova dominated the tiebreak.
"I didn't expect to win this one because I start a little bit bad," said Pliskova, whose last appearance in a semi-final came in Kuala Lumpur in February 2013. She went on to win that title.
"But she was playing amazing and I didn't have much chance to play my game. She was playing really fast. I also wasn't serving that high a percentage of first serves and that was the beginning of her game.
"I was trying in the second set to hold my serve and hoping that in the tiebreak anything can happen. In the third set I think she got discouraged. Losing the set from two match points and the tiebreak as well, it's bad."
Peng also let an opportunity slip away during her loss. She failed to capitalise on some break points, winning just one of seven while her opponent converted four of the seven she also held.
Although Hlavackova dominated the first set, breaking in the opening game and again to lead 5-2, she faced the prospect of a third set as Peng broke to lead 5-3 in the second before conceding the final four games.