The wins set up a mouthwatering clash between Pliskova, ranked five in the world, and number three Halep on the indoor hard courts of Ostrava on Sunday.
It is a second successive Grand Slam title for the Japanese, after her US Open triumph in September.
The Czech eighth seed downed the unseeded 17-year-old 6-2, 6-1 to set up a last eight meeting with either five-time Grand Slam champion Maria Sharapova or 15th seeded Australian Ashleigh Barty.
SYDNEY: Two-time Wimbledon champion Petra Kvitova avenged her US Open defeat to in-form Aryna Sabalenka Tuesday to move into round two of the Sydney...
The 22-year-old, who also reached the fourth round at the Australian Open earlier this year, ended Czech Kvitova's 13-match winning streak with a 7-6 (8/6), 7-6 (7/4) victory.
Petra Kvitova lost in straight sets 6-2, 6-4 to world No. 149 Amanda Anisimova.