Yamaguchi, who is ranked world number four, defeated an out-of-sorts Tai 21-9, 21-15 in a little over 30 minutes at Jakarta's Istora Senayan Stadium.
"This is my first Indonesian Open final — I'm very happy," Yamaguchi said after the match.
She will play India's Pusarla V. Sindhu.
The 25-year-old Tai said she was not feeling well and was unable to play at her best.
"Today I couldn't play at my usual speed," Tai said. "So my performance was hampered a little."
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World number three Chou Tien-chen of Taiwan was too strong for young Thai shuttler Kantaphon Wangcharoen in the men's singles, beating him 21-19, 18-21, 21-16.
Chou will play either Wong Wing Ki Vincent of Hong Kong or Denmark's Anders Antonsen in tomorrow's final.
In the men's doubles, Indonesian pair Mohammad Ahsan and Hendra Setiawan beat Japan's Takuro Hoki and Yugo Kobayashi 17-21, 21-19, 21-17, setting up an all-Indonesian final with Marcus Gideon and Kevin Sukamuljo.
Diminutive duo Gideon and Sukamuljo — affectionately dubbed the "Minions" after the little yellow characters featured in a popular 2015 animated film — are the world's top-ranked men's doubles pair and will be tough to beat.
They looked in ominous form against Li Jun Hui and Liu Yu Chen of China, crushing them 21-9, 21-13.
"Tomorrow's game is important for us," Gideon said. "We want to defend our championship title from last year."
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