Caroline Wozniacki ended Agnieszka Radwanska's Pan Pacific Open reign with a 4-6 7-5 6-4 victory in their semi-final encounter in Tokyo on Saturday.
Radwanska won the tournament in 2015 but will not have the chance to complete back-to-back triumphs as Wozniacki battled from a set down in a match that lasted close to three hours.
After dropping serve in game seven, the Pole won the next three to take the first set, though she needed three set points to move ahead of her resilient opponent.
Wozniacki, victor in 2010 and runner-up two years ago, trailed 3-1 and 5-3 before putting herself in position to serve out the set, which she had to do from deuce after squandering a 40-0 lead.
The Danish world number 28 secured a pivotal break in game seven of the decider, and, although she was unable to convert match point off Radwanska's serve, she booked her place in the final at the fourth attempt.
Wozniacki's opponent in the final will be Naomi Osaka, who also fought from behind to overcome Elina Svitolina 1-6 6-3 6-2.
Teenager Osaka will be featuring in her first WTA final and is the first Japanese finalist at this competition in 21 years.