The favourites won easily on the first day of the WTA Toray Pan Pacific event in Tokyo on Sunday,
No.14 seed Roberta Vinci defeated Barbora Zahlavova Strycova, 64 46 75 while No.12 seed Dominika Cibulkova got past Anabel Medina Garrigues, 63 76(3).
Former world no. 1 Jelena Jankovic and Croatian Petra Martic were also winners.
Local player Ayumi Morita lost the first seven games of her match but then went on to beat former top 10 player Andrea Petkovic 06 64 63.
Singles - First Round
(12) Dominika Cibulkova (SVK) d. Anabel Medina Garrigues (ESP) 63 76(3)
(14) Roberta Vinci (ITA) d. Barbora Zahlavova Strycova (CZE) 64 46 75
Jelena Jankovic (SRB) d. Yanina Wickmayer (BEL) 63 63
Petra Martic (CRO) d. Andrea Petkovic (GER) 06 64 63
(WC) Ayumi Morita (JPN) d. Sorana Cirstea (ROU) 62 36 62