The former world number one will be joined in the last four by either Elina Svitolina (2-0) or defending champion Caroline Wozniacki (1-1), who complete White Group play at the Singapore Indoor Stadium later on Thursday.
Kvitova (0-3) had lost her opening two matches and knew that only a straight sets victory would give her any chance of advancing but Pliskova (2-1) stayed calm and focused to record a first win over her compatriot in four attempts.
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"I cannot be more happy right now. It was a good match and she's a great player. She has always beaten me in the past but I knew I had a chance as I have been playing well," Pliskova said in a post-match interview.
"I'm not thinking about the next match yet, I'll do what I can to recover first. Before the tournament, I said to myself that I want to enjoy it and I will continue to do just that."
Kvitova needed to make a fast start to put her opponent under pressure but the double Wimbledon champion lacked movement and coughed up a slew of double faults to fall 4-0 down in the blink of an eye as Pliskova pounced on every opportunity.
Slowly but surely, Kvitova worked her way back into the contest, rallying twice from 40-0 down to win back-to-back games in the middle of the set that finally gave Pliskova something to think about.
Pliskova's coach Rennae Stubbs urged her to "stay disciplined" in the next changeover and the Czech heeded the advice to curb her attacking instincts as she ended Kvitova's tournament by holding serve to take the opener in 41 minutes.
The loss of the opening set appeared to free up Kvitova's booming forehand and she feasted on Pliskova's tentative start to the second set to race to a 3-0 lead, but the world number eight battled back brilliantly to book her semi-final place.
In the late match, Ukraine's Svitolina will advance if she wins one set against Wozniacki, who needs a straight-sets triumph to continue her title defence.
Barty fights back to beat Pliskova, will face Svitolina in last four
WTA Charleston, SC
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