Top seed Akane Yamaguchi battled back to reach the Badminton Asia Championships final with a controversial win over Indian rival P.V. Sindhu on Saturday.
Japan's Yamaguchi will be favourite to retain her women's singles crown when she faces China's unseeded Wang Zhiyi in the title-decider on Sunday in Manila.
Fourth-seeded Sindhu claimed the first game of her semi-final against the reigning world champion 21-13 and was leading 14-11 in the second when the umpire ruled that the Indian player was taking too long to serve.
A clearly unhappy Sindhu, an Olympic silver and bronze medallist, argued her case with the officials but to no avail and she conceded a point penalty to her opponent.
She appeared to lose her focus and rhythm after that, allowing Yamaguchi to come back to claim the second game 21-19 and the deciding third 21-16.
"That was one of the reasons I lost, that's my feeling. At that point it was 14-11 and you never know, it would have been 15-11," Sindhu said of the umpiring decision which proved to be a turning point in the match.
"It was very unfair, maybe I would have won the match and I would have played in the final."
Wang, the world number 16, booked her place in the final with a shock 10-21, 21-12, 21-16 victory over South Korea's second seed An Se-young.
The men's final will be between Malaysia's Lee Zii Jia and Jonatan Christie of Indonesia.
Third-seeded Lee swatted aside China's unseeded Weng Hongyang in ruthless fashion with a 21-11, 21-19 win in 39 minutes.
In contrast, fourth seed Christie was pushed to three games by his fellow Indonesian Chico Aura Dwi Wardoyo before prevailing 21-9, 18-21, 21-16 in just under an hour.