The 20-year-old Kazakh, who lost in the Shenzhen Open title clash last week, became the first player since Agnieszka Radwanska in 2013 to reach back-to-back finals in the opening two weeks of the year.
Standing in the way of Rybakina and a second career crown is fourth seed Zhang Shuai, who powered past Veronika Kudermetova 6-3 6-4 in the other semi-final.
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A bigger worry for the in-form Rybakina will be her fitness ahead of the Australian Open, which starts on Monday, as she twice needed treatment for her right leg late in the contest.
"I just pulled a muscle ... it happened to me for the first time and I was a bit scared because it's not a nice feeling," Rybakina told reporters.
"It was better after the treatment, I'll go away to the physio and try to recover."
Rybakina converted three out of four break points to claim the first set but 2015 champion Watson found a way back into the match by racing to a 5-1 lead in the second set and held off a late fightback by her opponent to draw level.
Despite struggling physically in the third set, Rybakina was able to hold her serve and broke a tiring Watson once more to secure the victory.
Earlier, Zhang sealed a spot in the third WTA singles final of her career with a clinical performance against fifth-seeded Russian Kudermetova.
She has the chance to seal a memorable double on Saturday after reaching the doubles final with partner Peng Shuai. The Chinese duo face Nadiia Kichenok and Sania Mirza next.
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