Osaka's victory in front of an expectant home crowd was her 10th in a row and did not look in doubt from the moment she pounded down a huge ace with her first serve of the match.
The 20-year-old, who became Japan's first ever Grand Slam singles champion in New York two weeks ago, hit a further eight aces to overwhelm world number 37 Giorgi.
Osaka has carried the poise and power that saw her overcome Serena Williams in the Flushing Meadows final across the Pacific with her and, helped by eight double-faults from Giorgi, wrapped up the victory in just 72 minutes.
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A runner up at this event two years ago, Osaka has not dropped a set so far this week and has had her service broken just once.
She will face world number eight Pliskova in the final after the Czech outlasted Croatia's Donna Vekic 6-2 4-6 6-3 in a topsy-turvy match that lasted over two hours.
Pliskova has spent more time on court than any other player at this tournament despite a first round bye and was once again dragged into a long contest by a dogged Vekic.
The former world number one started as if intent on finishing the contest as quickly as possible and stormed into an early 4-0 lead before wrapping up the first set in under half an hour.
Vekic, though, had defeated top 10 players Sloane Stephens and Caroline Garcia on route to the last four and recovered from an early break of serve in the second set to secure two breaks of her own.
Pliskova looked tired but dug deep in the third set and the quality of her superior hitting eventually told as she broke Vekic's resolve.
Currently just outside the top eight qualifying places for the WTA Finals in Singapore, Pliskova has now spent 420 minutes on court in Tokyo compared to 222 minutes for Osaka.
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