ORDER OF PLAY
Play starts at 10.45am
VOLVO CAR STADIUM
A Friedsam (GER) / S Sorribes Tormo (ESP) v  A Groenefeld (GER) / A Rosolska (POL)
Not before 1pm
 P Martic (CRO) v  C Wozniacki (DEN)
 M Keys (USA) v M Puig (PUR)
I Khromacheva (RUS) / V Kudermetova (RUS) vs  L Hradecka (CZE) / A Klepac (SLO)
Petra Martic is yet to taste victory in five previous meetings with Caroline Wozniacki, losing to the Dane each time in straight sets. Their most recent meeting came in Beijing last year, Wozniacki winning 7-5, 6-3 after almost two hours.
Martic is making her first appearance in a Premier-level semifinal and is the only one of the last four yet to win a career title. Trophy success for the Croat this weekend would make her the first Croat champion in Charleston since Iva Majoli in 2002.
Her run to the last four in Charleston will return the Croat to the Top 50, although she will not beat her career high rank of No.31, even if she wins the title this weekend.
Wozniacki hopes to replicate her 2011 success in Charleston, when she beat Elena Vesnina 6-2, 6-3. The Dane also made the final in 2009, losing to Sabine Lisicki.
Madison Keys would make her second final with victory on Saturday, the American previously taking part in the 2015 showpiece, where she lost to Angelique Kerber.
This weekend's eventual champion will be the 15th different winner from 15 different events on the WTA Tour in 2019, extending the record.
Read more: 14 different winners on Tour in 2019
Keys and Monica Puig are level at 2-2 in previous meetings, with the former winning the most recent encounter, at the French Open in 2016.
Puig is facing her third US seed in a week, having already knocked out Sofia Kenin and Danielle Collins.
Keys is seeking to reach her first final since the US Open two years ago. She would become the first American winner in Charleston in three years, since Sloane Stephens took the honors in 2016.
Keys and Martic have both been taken the distance twice this week, while Puig has not dropped a single set. Wozniacki was taken to three sets by Mihaela Buzarnescu in round three.
Read more: Charleston Previous Winners
Mild and overcast, with minimal chance of sunshine or rain. Maximum tempertaure 24C (75F).