But Pliskova snaffled an early break in the decider and hung on to reach her first Tokyo final, a forehand rocket ending her opponent's spirited resistance.
The 20-year-old Osaka has signed with the US$500,000 Hong Kong tournament to make her second straight appearance at Victoria Park and was scheduled to compete in this week's Wuhan Open in China.
"It's a bit surprising but I felt kind of calm going into the first round match and a lot of people were surprised because they thought I would be very nervous", Osaka told reporters of her stunning run of form.
"I just wanted to be patient and wait for my chances".
"She has basically every shot and she has a really good serve, so I know it will be a very hard match".
Pliskova's 11th WTA title took her past Kiki Bertens into the eighth and final qualifying place for the Porsche Race to Singapore.
The former world No.1, who spent 419 minutes on court en route to the final, celebrated her 11th title in 21 finals.
New Zealand's First Baby makes United Nations debut
When the event moderator remarked that the baby was backstage and very peaceful, Ardern quipped: "Wasn't at 3:30 this morning". Mr Gayford sent an image of his daughter's United Nations security pass, which playfully listed her title as "First Baby".
In her first semifinal since Madrid in May, saw off unseeded Vekic to seal her 14th three-set victory: only Kvitova (17), Sabalenka (17) and Halep (16) have won more.
Making fifth appearance at Tokyo, where she was through to the final for the first time, she battled back from 1-4 down in the final set against Gavrilova and came from a break down twice in the final set and saved two match points to defeat qualifier Riske in the quarter-finals.
"I'm just happy that I also have a title as a married woman".
In her postgame press conference, Pliskova said she had been wary of Osaka's power and had tailored a game plan aimed at neutralizing the U.S. Open champion's risky forehand.
For Pliskova, it was a first tournament victory since Stuttgart in April - and the first since wedding long-time partner Michal Hrdlicka in the summer. Pliskova said. "I feel like I'm improving in every match, but the opponents are always more tough".
In Sunday's final, Klizan will face the victor of the semi-final between top-seeded Austrian Dominic Thiem and fifth-seeded Spaniard Roberto Bautista Agut.
"I've literally never felt more exhausted in my entire life, so I kind of want to say the chances of me playing in the next tournament are very low", she said. "For a while it was looking like it maybe could be under two hours, but not really".