Naomi Osaka's dominant run came to end on Sunday in a 6-4, 6-4 loss to fourth-seeded Karolina Pliskova in the final of the Pan Pacific Open.

Playing in her first tournament since upsetting Serena Williams to win the US Open on Sept 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.

Pliskova came into Sunday's final having won her last four dating to the Brisbane International in January 2017 - and kept that streak alive while putting an end to Osaka's 10-match winning streak.

Pliskova needed three dramatic sets in each of her matches to reach her second final of the season.

Osaka started well with a pair of aces to win the opening game but Pliskova won her first break point of the match and took a 3-2 lead.

The 20-year-old local favorite was barely tested in her first three matches of the tournament but faced a much sterner challenge against Pliskova.

The frustration boiled over when Osaka double faulted in the ninth game of the second set to set up Pliskova's second break. The 20-year-old tossed her racket to the ground before collecting her composure, but it was too late.

Pliskova broke Osaka for a second time to go up 5-4 and then hammered her sixth ace to secure her 11th career title.

Osaka has been in the spotlight both on and off the court since arriving back in Japan after her historic win in New York.

Despite being encouraged by the sold-out crowd at Tachikawa Arena, Osaka wasn't able to stage a comeback. She finished with 26 unforced errors and admitted to being exhausted after the match.

"I've literally never felt more tired in my entire life," Osaka said. "To play the final of the US Open and then to come here, I think I did pretty well. So if there is anything I can take from this it is that I am proud of myself."