Muguruza is seeded No. 6 in the Tokyo tournament.
Also, Daria Gavrilova defeated Kristyna Pliskova 7-6 (2), 3-6, 7-6 (8), and Anett Kontaveit beat Kristina Mladenovic 6-3. 7-6 (5).
Caroline Wozniacki is the top-seeded player, and Caroline Garcia is No. 2. Both had byes in the first round and did not play Monday. Third-seeded Naomi Osaka, who won the U.S. Open just over a week ago, also had a bye in the first round.
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