Serving to stay in the match at 5-4 down in the second set, the writing appeared to be on the wall for Pliskova as she slipped 15-40 behind. Somehow, she served her way out of the cul-de-sac, saving both match points before going on to pinch the set on a tie-break.
Having dominated much of the first hour on court, Cirstea began to unravel in the decider. And as the unforced errors began to mount, Pliskova ruthlessly capitalized to wrap up the final set in just 27 minutes.
"I didn't expect to win," Pliskova said. "She was playing amazing in the first set and I didn't have any chance to play my game. She was playing fast and she was killing all my second serves. In the second set I was just trying to hold my serves and hoped that in the tie-break anything could happen."
Pliskova's 16 76(3) 60 win sees her advance to her first semifinal of the year, where she will face another unseeded player, Julia Goerges.
"I'm happy that I've won hard matches here," Pliskova said. "I played my last semifinal in Kuala Lumpur which is almost a year. So I'm happy that I'm not going to lose ranking points."
Like Pliskova, Goerges' progress was far from straightforward, coming from a break down in the final set to knock out No.5 seed Elena Vesnina.
Goerges had lost all three of her previous encounters with Vesnina and could have been forgiven for fearing the worst after dropping an opening set in which she had led 4-2.
However, the German showed admirable resolve to turn the match around, eventually running out a 57 63 63 winner.
"It was a pretty up and down match," Goerges said. "Elena is a great player and I knew it was going to be tough - I'd never beaten her before.
"I think I should have won the first set but I just kept fighting and I was serving really well today, which I think was key. I'm really glad I'm in the semifinals."
Hlavackova, who benefitted from the withdrawal of No.1 seed Sabine Lisicki earlier in the week, made a flying start against No.8 seed Peng Shuai but in the end was forced to dig deep to close out a 62 75 victory. No.4 seed Makarova meanwhile battled for more than two hours before eventually seeing off the stubborn resistance of Kimiko Date-Krumm, 62 46 64.