Osaka blasted seven aces against Japan's top-ranked player and converted two of five break chances.
The 18-year-old Osaka, who lost to Madison Keys in the third round of the U.S. Open, awaits the winner between Lucie Safarova and No. 6 seed Dominika Cibulkova.
French Open champion and top-seeded Garbine Muguruza has a first-round bye as does defending champion and second seed Agnieszka Radwanska.
Also, Monica Puig of Puerto Rico overpowered Vavara Lepchenko of the United States 6-0, 6-3.