( CNN ) -- There 's nothing worse than seeing your ex on top of the world while you 're down in the dumps . For two former halves of a sporting power couple , their fortunes could barely be more contrasting . While Danish tennis ace Caroline Wozniacki crashed out of the French Open in the first round , her former fiancee Rory McIlroy has been playing some of the finest golf of his career . The Northern Irishman broke off his engagement to Wozniacki on May 22 -- ending a three-year relationship -- before going on to win the European Tour 's flagship event -- the BMW PGA Championship -- on Sunday thanks to an imperious final-round 66 at Wentworth . McIlroy upped his game further on Thursday , posting a nine-under par opening round 63 at the Memorial Tournament in Ohio . The world No . 6 leads the field by three strokes , having missed out on the course record by two , and his stranglehold on the Jack Nicklaus event could have been even tighter had he not tweaked his left knee on the seventh hole . `` This has been coming , '' McIlroy , who will be attempting to win the U.S. Open for the second time in his career when it begins at Pinehurst on June 12 , told the PGA Tour 's official website . `` My performances have been really good , been shooting really good scores . There 's just been runs of holes in tournaments where I have n't played so well and I 've shot it four or five over in the space of nine holes , and that 's really just derailed my tournament . `` Last week I just did n't do that and that 's down to nothing more than hitting good golf shots and hitting good putts and limiting my mistakes whenever I get in trouble on the golf course . '' McIlroy showed little sign of being hampered by his knee injury , which was picked up during his second shot at the seventh . `` I wear spikes , so sometimes your foot can get stuck in the ground and you can torque your knee a little too much , '' explained the 25-year-old . `` I think that 's what I did , I tweaked it . The inside of it is sore , it 's a little swollen . I 'll go see the physio and get some treatment and get ice on it , and hopefully it will be OK for tomorrow . '' Double Masters champion Bubba Watson , his fellow American Chris Kirk and Englishman Paul Casey are in a three-way tie for second , one shot ahead of 2011 PGA Championship winner Keegan Bradley .
Rory McIlroy leads the Memorial Tournament by three shots after opening round . The Northern ##er shot an nine - under par 63 in Ohio City . The world No . 6 broke off his engagement to tennis star Caroline Wozniacki last week . Wozniacki was knocked out of the US Open in the first round earlier this week .