Americans Venus Williams and Sloane Stephens were among the winners Sunday on the first day of play at the Pan Pacific Open.
Williams cruised to a 6-3, 6-1 victory over Germany's Mona Barthel in just 64 minutes and, because of her unseeded status, will have to play top-seeded Victoria Azarenka in the second round. Azarenka, who had a first-round bye, has lost each of her two matches against the seven-time Grand Slam champion, but the two haven't met since the Dubai final in 2010.
The top seed in Tokyo would have been Venus' sister Serena, but the world No. 1 withdrew last week, citing fatigue.
Stephens, seeded ninth this week, eased past Switzerland's Stefanie Voegele, 6-3, 6-2.
Other seeded winners Sunday were Samantha Stosur, Kirsten Flipkens, Sorana Cirstea and Dominika Cibulkova.
The 12th-seeded Stosur rallied for a 2-6, 6-4, 6-1 triumph over France's Alize Cornet, while the 14th-seeded Flipkens battled past Barbora Zahlavova Strycova of the Czech Republic, 7-6 (7-4), 7-5. Cirstea, the 15th seed, topped German Julia Goerges, 6-4, 6-4, and the 16th-seeded Cibulkova dumped Poland's Urszula Radwanska, 6-3, 6-3.
Two-time Grand Slam champ Svetlana Kuznetsova was an unseeded winner, thumping Argentina's Paula Ormaechea, 6-1, 6-2. Next up for the Russian veteran will be third-seeded Sara Errani.
Four other unseeded winners Sunday were Elina Svitolina of the Ukraine, Lucie Safarova of the Czech Republic, Spain's Maria-Teresa Torro-Flor and Switzerland's Belinda Bencic.
The first round will conclude on Monday, while second-round play also begins with matches for fifth-seeded Angelique Kerber, seventh-seeded Petra Kvitova and eighth-seeded Roberta Vinci.