Having knocked out Australian Open champion Sofia Kenin in the first round, the 20-year-old Rybakina struck 33 winners and 11 aces to oust Pliskova for the first top-five win of her career.
"I didn't really think if she's number two (or) three, doesn't really matter for me," Rybakina said. "I always try to do my best.
"I thought that I will have problems with the serve because indoors it's a different feeling. I'm surprised with my serve, that I'm really doing good."
Pliskova said she "didn't do that much wrong" on the day but Rybakina was on point, winning 80% of her first serve points and firing powerful winners past her Czech opponent.
On the other side of the draw, American qualifier Jennifer Brady -- playing her sixth match in Dubai in six days -- upset Garbine Muguruza 6-7(5) 6-3 6-4 to advance to her first semi-final at WTA Premier level.
Muguruza fought back from 3-5 down to take the opening set to a tiebreak. But her intensity dropped halfway through the second set and Brady was too strong for the Australian Open finalist on crucial points in the decider.
"I think the match started from 3-2 in the second set for me," said Brady, whose notable scalps this year include world number one Ash Barty.
Romanian Halep, who was unable to cope with Sabalenka's power at the start of the match, played quicker in the final two sets.
"I think I started to play a little bit stronger in the second set and find rhythm," Halep said.
"Always it's tough against her because she's a little bit taller than me and she has a lot of power. I just had to block some balls, and to get the initiative to go and open the court."