Former women’s tennis world number one Ana Ivanovic admitted Saturday she retired this week because she felt both physically and mentally unfit to carry on after years of battling injuries. The 29-year-old Serbian — whose sole Grand Slam success came in the 2008 French Open one of her 15 WTA titles — added she wanted to retire while she still loved the sport. “The last few years have been a struggle with injury,” Ivanovic told The Times newspaper on Saturday.