ISTANBUL, Turkey - No.3 seed Agnieszka Radwanska's quest to add a second career title at the TEB BNP Paribas Istanbul Cup a decade after her first ended in injury on Tuesday, as the World No.29 was forced to retire in her opening round match against Donna Vekic.

The 2008 champion in Istanbul lost eight of the first nine games of the match before shaking hands, as Vekic advanced to the round of 16 with a 6-1, 2-0 victory. 

"I was really happy with the way I played. I thought I started really well...I was aggressive, trying to move her and serving well," Vekic said after the match.

"It was very unfortunate that it had to finish that way and that she had some back pain. I had the same a few weeks ago and it's not easy, so I hope she will get better."

While victory did not come in a way she would've liked, the World No.54 improved to 6-4 in first round matches in 10 tournaments played this year, and scored her best victory in terms of ranking since defeating then-World No.24 Peng Shuai in the second round of last summer's US Open.

"Even if I lose sometimes, I'm really happy with my level these past few weeks," Vekic said. "I know I keep improving and my game is there. My expectations for clay are never really high. I played better on clay last year so that gave me some confidence.

"I know I play heavy and when I have time, I can play good. I'm really happy with the way I played today and how I moved."

In other first round action in Istanbul on Tuesday, No.4 seed Zhang Shuai and No.6 seed Sorana Cirstea both fell at the opening hurdle.

Zhang was upset by Dutch qualifier Arantxa Rus, 6-2, 6-3, while Cirstea came out on the losing end of an up-and-down encounter against Yulia Putintseva, 0-6, 6-1, 6-0. 

However, No.7 seed Irina-Camelia Begu managed to avoid the upset bug, as she won the last 11 games and saved four set points in the first set to defeat Slovenian qualifier Dalila Jakupovic, 7-5, 6-0.