Multiple choice general knowledge sports Federer won which grand slam only once? Wimbledon French Open Australian Open US Open Reveal answer Fill a bubble to check yourself B Correct answer Explanation Federer won the French Open only once in his career (2009), completing his career Grand Slam. In contrast, he won Wimbledon 8 times, US Open 5 times, and Australian Open 6 times. The clay surface at Roland Garros was his most challenging major.