After taking a fall in the Fed Cup semi-finals, Simona Halep will miss the Stuttgart Open this week.
Tamara Zidansek took the first set off Petra Martic in Istanbul, but the sixth seed fought back to reach the second round.
Simona Halep could not inspire Romania to doubles success in the decider as France booked a Fed Cup final date with Australia.
Romania and France are level at 1-1 in their Fed Cup semi-final after wins for Simona Halep and Caroline Garcia in Rouen on Saturday.
Aryna Sabalenka and Ashleigh Barty will meet in a potentially pivotal showdown on Sunday after winning their opening matches.
Former world number one Maria Sharapova is a three-time Stuttgart Open winner but she is not fit enough to fight for the title next week.
Germany will be without Angelique Kerber as they look to preserve their Fed Cup World Group place against Latvia this weekend.
Sascha Bajin, the WTA's Coach of the Year for 2018 following his work with Naomi Osaka, has been hired by Kristina Mladenovic.
In a Bogota Open final between two rising stars, 17-year-old Amanda Anisimova outlasted Astra Sharma on Sunday.
Polona Hercog won a back-and-forth contest against Iga Swiatek to win the Ladies Open Lugano.