Boulter, 22, won 6-3, 1-6, 6-3 against Krejcikova, who is currently No. 2 in the world doubles rankings, to back up her career-best win over world No. 42 Maria Sakkari earlier in the week.
She is now set to enter the world's top-100 for the first time, regardless of the outcome of her match against world No. 6 Pliskova in Friday's quarterfinal.
No. 2 seed Carolina Garcia also advanced to the last eight after a 6-3, 6-4 win over China's Yuxuan Zhang. No. 3 seed Elise Mertens was another comfortable victor as she defeated Jana Cepelova 6-3, 6-3.