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. Ana Ivanovic was world number one for a spell in 2008, the same year she won her sole Grand Slam title at the French Open 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.