Zheng hit 33 winners and fired off 16 aces in Tokyo on Sunday as she took the 7-6 (7-5) 6-3 victory in an hour and 52 minutes under a closed roof after heavy rain interrupted the first set.
The 22-year-old adds the Tokyo title to her wins in Palermo and the Paris Olympics this year.
The first set was a tightly fought encounter without a single break of serve, with Zheng failing to convert five break points. However, she was much more clinical in the tiebreak and clinched it with a vicious forehand winner.
The second set played out much differently as Zheng held to start and broke for 2-0 when Kenin netted a backhand, before consolidating that break to go 3-0 up.
Kenin, playing with her right thigh strapped, refused to go quietly and forced Zheng to defend her first break point of the match, but the power and precision of the Chinese world No.7's serve proved too much for the American.
China's Zheng Qinwen (left) and American Sofia Kenin shake hands after the final in Tokyo. (AP PHOTO)
Zheng's win improved her record at the Pan Pacific Open to 8-1, with the 22-year-old having lost in the 2022 final to Russia's Liudmila Samsonova in her only previous appearance at the tournament.
It also ensured her a first hard-court title since her Zhengzhou Open win last year, and will give her a boost in confidence ahead of next month's season-ending WTA Finals in Saudi Arabia.
"I want to say congratulations to you," Zheng said of Kenin.
"You did a great job, I saw you were taped up and played though you were hurt. I know this feeling. You fought so hard on the court."
Despite the loss, 2020 Australian Open champion Kenin can take plenty of positives from her performance in Tokyo, where she dropped just one set en route to the final, beating world No.9 Daria Kasatkina along the way.
Kenin, 25, also finished runner-up at the French Open in 2020 and reached a career-high No.4 that season, before injuries, illness and off-court issues saw her drop down the rankings.
"I would like to thank the tournament director for giving me the wild card. I really appreciate it," Kenin said.
"Unfortunately, I couldn't get the title today, but I'm very happy with the week I had."Â
17°C