Johanna Konta leads the head-to-head against No.2 seed Hsieh Su-Wei 4-2, though the pair are tied on clay at 1-1. Hsieh's 1-6, 7-6(2), 6-4 upset of the Briton in the first round of Roland Garros 2017 was her first career Top 10 win at the age of 31, but arguably kickstarted a career as a giantkiller - since that match, the Chinese Taipei player has tallied another five Top 10 victories. However, she has won just 10 games from Konta in three subsequent matches, including a 6-0, 6-4 loss in Rome last year and a 6-0, 6-2 defeat in the second round of Indian Wells this March.
Hsieh will be bidding for the second claycourt semifinal of her career, following Rabat last year; Konta will be looking to make her debut in the last four of a WTA event on the terre battue.
Defending champion Elise Mertens and Maria Sakkari are old ITF Pro Circuit foes: the pair met three times in 2014, with the Belgian taking two ITF W10 encounters in Tinajo and an ITF W50 match in New Delhi, while Sakkari triumphed in an ITF W25 first-round tilt in Sharm el Sheikh. Two years later, the Greek would also win their Australian Open qualifying bout 2-6, 6-4, 6-2 - but despite both progressing into the Top 30 since those days, they have never previously met in a WTA main draw match. Today's encounter will also be their first clay meeting.
Last year's runner-up Ajla Tomljanovic is 3-1 against Rebecca Peterson, including their most recent match 6-3, 6-3 in the second round of Mallorca last year. The Swede's only victory came 7-5, 7-6(3) in the Honolulu 125K quarterfinals in 2017; this will be the first time the pair have played on clay.
An all-Belgian derby will find No.8 seed Alison Van Uytvanck taking on qualifier Ysaline Bonaventure for the first time. Van Uytvanck is 2-4 against her compatriots in WTA main draws, while Bonaventure - who is playing the second WTA quarterfinal of her career following Budapest 2018 - lost her only previous WTA main draw match against a countrywoman to Maryna Zanevska in Bucharest last year.
ORDER OF PLAY
CENTRE COURT (starts 11am)
[Q] Ysaline BONAVENTURE (BEL) vs Alison VAN UYTVANCK (BEL) 
Rebecca PETERSON (SWE) vs Ajla TOMLJANOVIC (AUS) 
Johanna KONTA (GBR)  vs HSIEH Su-Wei (TPE) 
[WC] Elise MERTENS (BEL)  vs Maria SAKKARI (GRE) 
COURT 1 (starts 1pm)
María José MARTÍNEZ SÁNCHEZ (ESP) / Sara SORRIBES TORMO (ESP)  vs Alexa GUARACHI (CHI) / Sabrina SANTAMARIA (USA) 
[WC] Ana BOGDAN (ROU) / Isabella SHINIKOVA (BUL) vs Georgina GARCIA PEREZ (ESP) / Oksana KALASHNIKOVA (GEO)