No.1 seed Naomi Osaka will make her second appearance in her city of birth this year. The Australian Open champion previously competed in the Japan Women's Open in 2014 - the International tournament's final year in Osaka before moving to Tokyo and then Hiroshima - as a 16-year-old wildcard, reaching the second round before falling to Elina Svitolina in three sets.
No.9 seed Elise Mertens is 1-1 against Hsieh Su-Wei, with both of their matches taking place in 2018. Mertens won the only completed one 6-0, 6-2 in the Rabat semifinals, but retired trailing 2-6, 0-4 in the Tianjin quarterfinals.
No.4 seed Angelique Kerber is bidding to snap a five-match losing streak stretching back to the second round of Wimbledon, where her title defence was ended at the hands of Lauren Davis. Since then, the three-time major champion has lost two matches despite bagelling her opponent - to Daria Kasatkina in Toronto and Kristina Mladenovic at the US Open - and once more from match point up, to Alison Riske in Zhengzhou.
Qualifier Nicole Gibbs is seeking her first career win over a Top 20 player against Angelique Kerber. The American has stretched rivals in that echelon to three sets on three occasions - Petra Kvitova at Indian Wells 2016, Karolina Pliskova at the 2017 US Open and Simona Halep at this year's US Open - but her best career win by ranking was over World No.24 Madison Keys in the second round of Indian Wells in 2016.
No.5 seed Madison Keys was a 7-6(5), 6-1 victor in her only previous encounter with qualifier Zarina Diyas, in the first round of the 2016 Australian Open. Diyas is looking for her first Top 20 win since 2015, when she defeated Andrea Petkovic to reach the fourth round of Wimbledon.
ORDER OF PLAY (all courts start 11am)
[Q] Nicole GIBBS (USA) vs  Angelique KERBER (GER)
Not before 12.30pm
 Madison KEYS (USA) vs [Q] Zarina DIYAS (KAZ)
HSIEH Su-Wei (TPE) vs  Elise MERTENS (BEL)
Not before 5pm
 Naomi OSAKA (JPN) vs [Q] Viktoriya TOMOVA (BUL)
 Nicole MELICHAR (USA) / Kveta PESCHKE (CZE) vs Nadiia KICHENOK (UKR) / Abigail SPEARS (USA)
 Anna-Lena GROENEFELD (GER) / Demi SCHUURS (NED) vs [WC] Momoko KOBORI (JPN) / Ayano SHIMIZU (JPN)
Misaki DOI (JPN) / Nao HIBINO (JPN) vs Francesca DI LORENZO (USA) / Katarzyna KAWA (POL)
Alicja ROSOLSKA (POL) / Dayana YASTREMSKA (UKR) vs HSIEH Su-Wei (TPE) / HSIEH Yu-Chieh (TPE)