Wozniacki held a 5-0 lead in the second set before Osaka staged a brief rally. Her victory was complete when Osaka hit a return wide.
"I just fought for every point and tried to stay aggressive and make her move," Wozniacki said afterward. "She fought back in the second set so I was just happy to close it out."
Wozniacki, from Denmark, won the event for the second time, also prevailing in 2010.
She is also trying to make the best of a trying season in which she has dealt with ankle and wrist injuries. She took a medical timeout during the first set due to groin soreness.
"I'm enjoying it at the moment," said Wozniacki, who recently reached the U.S. Open semifinals. "Injuries happen and you never know when you can be taken out of the game, so I'm just enjoying every minute."
Spain's Lara Arruabarrena recorded her second career WTA title with a 6-0, 2-6, 6-0 victory over fifth-seeded Monica Niculescu of Romania at the Korea Open in Seoul, South Korea.
Arruabarrena rolled through the first set unblemished before Niculescu controlled the second. She recovered in the third with her second unbeaten set to claim the crown.
Arruabarrena's other WTA victory came in 2012.