Tokyo
The 12th-ranked Bencic beat Marketa Vondrousova of the Czech Republic 7-5, 2-6, 6-3 for the first major title of her career.
Bencic will also contest the women's doubles gold-medal match on Sunday.
Bencic and Swiss partner Viktorija Golubic face the top-seeded Czech team of Barbora Krejcikova and Katerina Siniakova.
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