Lucie Safarova needed three sets to beat Madison Keys at the WTA event in Tokyo while Belinda Bencic was also amongst the winners.
Lucie Safarova of the Czech Republic rallied from a set down to beat American teenager Madison Keys 6-7 (7-4) 6-4 6-2 in the first round of the Pan Pacific Open on Monday.
The seventh-seeded Safarova saved eight of 10 break points to oust the unseeded Keys and advance to the second round, where she will face wildcard entry Belinda Bencic of Switzerland.
Bencic defeated Svetlana Kuznetsova of Russia 6-3 6-0.
Top-seeded Angelique Kerber of Germany has a first-round bye, as does second-seeded Caroline Wozniacki of Denmark, who won the event in 2010.
In other first-round matches, Elina Svitolina of Ukraine defeated Barbora Zahlavova Strycova of the Czech Republic 6-4 6-1, while Garbine Muguruza of Spain beat Anastasia Pavlyuchenkova of Russia 6-3 7-6 (7-3).