* Sobbing Dokic retires with back injury while leading
* Dementieva says she did not deserve to go through
By Sonia Oxley
PARIS, May 28 (Reuters) - Jelena Dokic left the court in floods of tears on Thursday after retiring with a back injury while leading by a set in her French Open second round match against Russian fourth seed Elena Dementieva.
"It's a shock and a disappointment," the Australian former world number four told a news conference after quitting with the score at 6-2 3-4 against.
"I felt like I had the match in my hands and I was doing well and even if I didn't win, I was playing really well ... I felt like I probably played the best tennis that I played this year."
Dokic, appearing at her first French Open since 2004, appeared to pull something in her lower back at 2-2 in the second set and went off court to receive treatment from the tournament trainer.
She returned to break Dementieva despite crying between points.
"I just went down and couldn't come back up. I don't know what it is yet. It was very painful, and I just hope it's not too serious," said Dokic, who sobbed uncontrollably into her towel after retiring while Dementieva came over to comfort her.
Dokic, who rolled her ankle in her last-16 match at the Australian Open, said she was not having much luck at the grand slams on her comeback trail after a troubled few years.
"Obviously it's not my time at the grand slams," said Dokic. "I'm not 15 anymore, so it's time probably to take more care now and I just really, really hope it's nothing serious.
"I was supposed to play doubles tomorrow. I don't think that will happen."
Dementieva was full of sympathy for her opponent.
"It feels bad to win this way and it must be hard on her. She was very solid it's bad luck for her," the Russian, who next faces Dokic's compatriot Samantha Stosur, told reporters.
"I didn't deserve to win this match." (Editing by Pritha Sarkar; To query or comment on this story email email@example.com)