Play starts at 11.30am
Madison KEYS (USA) v Anastasia PAVLYUCHENKOVA (RUS)
[WC] CoCo VANDEWEGHE (USA) v Sloane STEPHENS (USA) 
Kristina MLADENOVIC (FRA) v Anett KONTAVEIT (EST)
Not before 6.30pm
Petra KVITOVA (CZE)  v Angelique KERBER (GER)
Simona HALEP (ROU)  v Magdalena RYBARIKOVA (SVK)
Shuko AOYAMA (JPN) / Miya KATO (JPN) v Kiki BERTENS (NED) / Demi SCHUURS (NED) 
[Q] Veronika KUDERMETOVA (RUS) v Carla SUAREZ NAVARRO (ESP)
[LL] Carina WITTHOEFT (GER) v [Q] Zarina DIYAS (KAZ)
Not before 4pm
Antonia LOTTNER (GER) / Lena RUEFFER (GER) v Jelena OSTAPENKO (LAT) / Olga SAVCHUK (UKR)
Bethanie MATTEK-SANDS (USA) / CoCo VANDEWEGHE (USA) v Arantxa PARRA SANTONJA (ESP) / Katarina SREBOTNIK (SLO)
Not before 8pm
Raquel ATAWO (USA) / Anna-Lena GROENEFELD (GER)  v Monique ADAMCZAK (AUS) / Lyudmyla KICHENOK (UKR)
Keys is seeking her 160th career main draw victory today.
Vandeweghe v Stephens is the Miami Open doubles champion v the Miami Open singles champion respectively.
Mladenovic was last year's runner-up in Stuttgart.
The Frenchwoman has never played Kontaveit before.
Halep begins her campaign to become the first World No.1 to win the title in Stuttgart since Justine Henin in 2007.