"I have literally never been so exhausted in my entire life", she told reporters.
"Naomi was playing so good the whole tournament, the future is bright".
Osaka served notice of her intentions as she started the match with a huge ace - but a netted backhand in her third service game handed Pliskova the crucial break in what would prove to be the only break point of the first set.
Playing in her first tournament since upsetting Serena Williams to win the U.S. Open on September 8, third-seeded Osaka hadn't dropped a set previous to Sunday's final but was frustrated from the outset by the big-serving Czech player. But I served really well and that got me out of a lot of trouble today.
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 unsafe forehand.
Former World No.1 Pliskova was on fire in the opening set dominating the rallies.
Pliskova has had tough matches all week, having saved two match points against American qualifier Alison Riske in the last round, then fighting back from a set down to get past Daria Gavrilova, earlier in the tournament.
Pliskova's win ends an incredible run by Osaka that saw her take the U.S. Open and roar through the Pan Pacific draw unscathed as the buzz over her grand slam win reverberated across the country. Within hours of her 6-4, 6-4 defeat in Tokyo, Wuhan Open organisers said on Twitter she withdrew from their tournament, citing a "viral illness".
When asked to explain her lackluster performance, Osaka replied: "If I know I would have fixed it". She's 0-3 in finals for her career.
Currently just outside the eight qualifying spots for next month's WTA Finals in Singapore, Pliskova has now spent 420 minutes on court in Tokyo compared to 222 minutes for Osaka.
A tearful Osaka could barely bring herself to speak at the trophy presentation.
"I didn't want to try to overpower her because I think she just has more power than me, so I just wanted to be patient and just to wait for my chances, waiting for my shots", Pliskova said.
"The chances of me playing in the next tournament are very low".