Caroline Wozniacki, without a crown since March last year, overcame a leg injury to claim a 7-5 6-3 win over Naomi Osaka in Tokyo on Sunday.
Wozniacki, champion of the event in 2010 and runner-up in 2014, needed treatment during the first set.
But she battled it out before Osaka also needed medical attention, the Japanese teenager getting her shoulder treated.
Wozniacki had twice come from a break down in the first set, but she rolled out to a 5-0 lead in the second.
Osaka, in her second WTA final, recovered with some incredible power to win the next three games, but Wozniacki closed it out to love in the ninth game.
The title was the 24th of Wozniacki’s career, while Osaka is now 0-2 in finals, having also been beaten in the Hua Hin decider last year.