US Open champion Samantha Stosur survived a scare against Thai qualifier Noppawan Lertcheewakarn at the HP Open on Tuesday.
The top-seeded Australian was expected to steamroller the world number 168 but it turned out to be a much closer first-round match than most had predicted in Osaka.
Stosur dropped the second set against the former Junior Wimbledon champion before recovering to win 6-3 3-6 7-5 in over two hours.
Third seed Angelique Kerber had a much easier time against home hope Kurumi Nara, dropping just three games, while fourth seed Petra Cetkovska edged out veteran Japanese Kimiko Date-Krumm 6-2 7-6 (7/2).
On a day of few surprises, fifth seed Jarmila Gajdosova and sixth seed Ayumi Morita also advanced.
Australian Gajdosova beat Aiko Nakamura 6-0 6-1 and Nakamura's countrywoman Morita beat Zhang Shuai 7-6 (7/3) 6-2.
There were also wins for Zheng Jie, Olga Govortsova, Erika Sema and Yaroslava Shvedova.