Today's semifinal between No.8 seed Anastasija Sevastova and No.5 seed Julia Goerges will be the eighth iteration of a rivalry that dates back a decade. The German leads the head-to-head 4-3, although one of her wins came via retirement.
Both Sevastova and Goerges enjoyed career-best years in 2017, and have faced each other three times in the past 10 months - with Sevastova triumphing 6-4, 3-6, 6-3 in the Mallorca final on grass and 6-3 6-3 in Indian Wells on hard courts a month ago, and Goerges taking their Zhuhai Elite Trophy semifinal 6-3, 6-3. The Latvian was also victorious in their only previous clay encounter - their very first match in 2007, in the qualifying of the ITF $25,000 event in Prague.
No.12 seed Kiki Bertens was the winner in her only meeting to date with No.7 seed Madison Keys - also on clay, in the fourth round of Roland Garros in 2016, with a 7-6(4), 6-3 scoreline.
Madison Keys is aiming to reach her eighth career final and third on clay; the runner-up here in 2015 to Angelique Kerber, she is the only remaining player to have been to the Charleston final before. Kiki Bertens is shooting for her sixth career final, and first at Premier level; all of her previous five have been clay Internationals.
Julia Goerges will bid for her 12th career final - and seventh in the past 10 months, which would tie Caroline Wozniacki for the most title rounds reached in that time frame. Anastasija Sevastova is going for her fifth career final, and first at Premier level.
If Kiki Bertens defeats Madison Keys today, it would break a streak of 10 consecutive losses to Top 20 opponents for the Dutchwoman dating back to last July, when she beat Timea Bacsinszky in the Gstaad semifinals.
In doubles, Andreja Klepac and María José Martínez Sánchez are shooting for their fourth final as a team, and third of 2018 following Brisbane and Doha. Their opponents, Mihaela Buzarnescu and Heather Watson, teamed up for the first time this week.
ORDER OF PLAY (starts 10.45am)
VOLVO CAR STADIUM
Mihaela BUZARNESCU (ROU) / Heather WATSON (GBR) vs  Andreja KLEPAC (SLO) / María José MARTÍNEZ SÁNCHEZ (ESP)
Not before 1pm
 Julia GOERGES (GER) vs  Anastasija SEVASTOVA (LAT)
 Kiki BERTENS (NED) vs  Madison KEYS (USA)
Kateryna BONDARENKO (UKR) / Aleksandra KRUNIC (SRB) vs Alla KUDRYAVTSEVA (RUS) / Katarina SREBOTNIK (SLO)