The newly-crowned US Open champion, who was bidding to become the first Japanese victor of the event since 1995, succumbed 6-4 6-4 in a battle of two big servers.
"It was important for me to play just two sets and not go to a third one".
"My serve is my biggest weapon and it was key today", added Pliskova after scooping an 11th career title. "Naomi was playing so good all tournament but I think she was a little bit exhausted today".
Pliskova took advantage, capitalising both times when presented with a break point and winning the last 11 points to secure her second WTA title of the campaign.
The Wuhan Open, which began on Sunday and ends on September 29, still boasts a strong field despite Osaka's withdrawal, with the top five women's players, including world number one Simona Halep, all taking part.
Fourth seed Pliskova was pushed hard by Vekic before winning 6-2, 4-6, 6-3 for a spot in Sunday's final. Osaka was caught flat-footed and dumped it into the net.
The 20-year-old, who became Japan's first Grand Slam singles champion in NY two weeks ago, hit a further eight aces to overwhelm world number 37 Giorgi.
Osaka could not recover after being broken by the world number eight in the fifth game of the first set and, as the strain began to show, she called for coach Sascha Bajin and groaned: "I feel so stressed out".
Osaka, supremely confident and in top form coming into the contest on the back of 10 consecutive wins, appeared uncertain throughout the match as her Czech opponent broke serve once in each set to triumph in 64 minutes.
The 20-year-old, looked at a loss for ideas against Pliskova, six years her senior, and buried her head in a towel during the changeover. "I was getting exhausted from the match, so it was not as fast as I wanted to serve".
Pliskova then served out the match with a love game, sealing the victory with an ace. "I'm just happy that I also have a title as a married woman".
"I know that she's a great player", Osaka said of Pliskova.
"I've never felt more exhausted in my entire life", she said, admitting that a much-needed rest was in order.
With her second title at the tournament, Wozniacki became the fifth player in the 2000s to win the event a couple of times.