(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 haven'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 didn'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.