No.8 seed Laura Siegemund and qualifier Patricia Maria Tig face each other in a rematch of this year's Bucharest semifinal, won by Tig 6-3, 6-1 to reach her second career final. It was the Romanian's first win in three attempts against Siegemund, who was the victor in a pair of 2016 matches in the first rounds of Charleston and the US Open.
No.6 seed and 2017 champion Zarina Diyas leads the head-to-head against Nao Hibino 2-1, although the pair have not played each other in six years. All of their previous meetings have also been in Japan: Hibino took the first 6-2, 6-3 in the first round of an ITF 25K event in Noto in 2012, but the following year Diyas won both their Osaka qualifying clash and their Makinohara ITF W25 semifinal for the loss of just eight games across the two matches.
No.1 seed Hsieh Su-Wei is aiming to defend a WTA title for the first time. The Chinese Taipei player's previous two title defenses were ended in the quarterfinals of Kuala Lumpur 2013 by eventual runner-up Bethanie Mattek-Sands and in the second round of Guangzhou 2013 by eventual champion Zhang Shuai. Hsieh takes on Priscilla Hon for the first time; the Australian is bidding for a first Top 50 win and a second WTA quarterfinal following Seoul 2017.
No.2 seed Veronika Kudermetova, who made her Top 50 debut in this week's WTA Rankings, is aiming to reach her sixth WTA quarterfinal of the season today; opponent Christina McHale, the 2016 champion and former World No.24, is seeking to reach the last eight of a WTA tournament for the first time since Tianjin 2017.
ORDER OF PLAY (all courts start 11.30am)
Nao HIBINO (JPN) vs  Zarina DIYAS (KAZ)
 HSIEH Su-Wei (TPE) vs Priscilla HON (AUS)
Christina MCHALE (USA) vs  Veronika KUDERMETOVA (RUS)
 Laura SIEGEMUND (GER) vs [Q] Patricia Maria TIG (ROU)
Miyu KATO (JPN) / Storm SANDERS (AUS) vs  Mihaela BUZARNESCU (ROU) / Katarina SREBOTNIK (SLO)
Misaki DOI (JPN) / Nao HIBINO (JPN) vs  Kirsten FLIPKENS (BEL) / Alison VAN UYTVANCK (BEL)
Haruka KAJI (JPN) / Junri NAMIGATA (JPN) vs Priscilla HON (AUS) / Tatjana MARIA (GER)