Kim Clijsters won the battle of the former world number ones as the Belgian defeated Serbia\'s Ana Ivanovic 6-3, 6-4 to reach the quarter-finals of the Olympics on Wednesday. Clijsters is playing the penultimate tournament of her career as she prepares to retire for the second and final time after next month\'s US Open and she has admitted an Olympic medal would be the perfect way to sign off. The 29-year-old, competing in the Olympics for the first time, remains on course to fulfill that dream after cruising past former French Open champion Ivanovic in 58 minutes at Wimbledon. Four-time Grand Slam champion Clijsters, ranked 36th, will face world number three Maria Sharapova or Germany\'s Sabine Lisicki in the last eight.