Facing the 24-year-old local hope for the first time, Garcia dropped her serve in the opening game but rallied to claim the next five games, including a run of 11 points in a row.
The pair exchanged early breaks in the second set but Garcia took a decisive lead at 4-3 and went on to seal victory in 90 minutes.
"It's never easy to play someone you never played before," French number one Garcia said.
Pliskova sets up Tianjin final with Garcia
"She had nothing to lose, and she was hitting the ball very well, especially from the backhand side."
The 24-year-old will next face sixth seed Petra Martic.
"I played her in Madrid this year," said Garcia, who beat Martic 6-3 7-5 in the Spanish capital. "She has a good serve and a good forehand, so I'll have to play my best and see what I can do."
Third seed Elise Mertens secured an impressive 6-2 6-3 victory over Slovakian Jana Cepelova and the Belgian will face Taiwan's Hsieh Su-wei in the last eight.
Boulter knocked out by top seed Pliskov
Boulter continues fine run by overcoming Krejcikova in three