 Complete the following phrase:  Juan Martín del Potro and Roger Federer have played 25 times, with Federer leading 187. They have met seven times in Grand Slam tournaments, with Federer leading 52. Their two most famous Grand Slam tournament meetings came in 2009. The first was in the French Open semifinals, when Federer survived a five-set clash when he was on his way to the only French title of his career. The second was in the final of the US Open, where del Potro beat five-time defending champion Federer in five sets, ending his 20-match winning streak at Grand Slams. Another high-profile match was in the semifinals of the 