Rory McIlroy continued to show no mental scars from a tough week in his private life to fire a sublime nine-under par 63 at Muirfield Village to move into an early three-shot lead, despite injuring his left knee mid-round.
Having won last week's BMW PGA Championship at Wentworth in the immediate aftermath of his announcement that he had broken off his engagement to professional tennis player Caroline Wozniacki, the Northern Irishman was once again in superb form as he mixed seven birdies with two eagles and a sloppy double bogey at 14.
He leads by three at the top in Dublin ahead of England's Paul Casey and the American duo of Chris Kirk and Masters champion Bubba Watson who all enjoyed six-under 66s.
The US trio of Michael Thompson, J.B. Holmes and Keegan Bradley lie a shot further back at five under. Bradley was the early talk of the tournament after the 2011 US PGA winner surprised the crowd by ditching his anchor putter for a conventional flat stick before carding a bogey-free 67.
World number one Adam Scott managed a three-under 69, the same score shot by 20-year-old American sensation Jordan Spieth. Luke Donald shot 71 to lie eight back of McIlroy, while Justin Rose struggled to one over and will need a much improved round on Friday if he's to make the weekend.
The same can be said of defending champion Matt Kuchar who failed to replicate some of the form he's shown so far this year with a 74.
McIlroy had no problems continuing the excellent form he's shown in 2014, though. The 25-year-old from Holywood has only finished outside the top 10 once all season in the 10 stroke play events he has started - a trend that, barring a dramatic collapse over the next three days, looks set to continue.
The world number six got off to the perfect start as he made immediate in-roads at holes two and four to quickly move into the red. However, despite making another birdie at the par-five seventh, McIlroy revealed after that he injured his left knee on his approach to that hole.
If it was painful, he certainly showed no signs of it as he reached the turn in 32 and made a back-nine assault on the Jack Nicklaus-designed 18 holes.
A birdie-eagle start at 10 and 11 took the Northern Irishman into the solo lead for the first time and another birdie followed at 13. Unfortunately, the only blemish on his card came at the next and it was a costly mistake, too, as a poor lie in a green side bunker led to a double-bogey six to fall back into a share of first.
The two-time major winner merely shrugged the error off, however, as he made his second eagle of the day - this time at 15 - thanks to a fine driving display complemented by some powerfully accurate iron play. His putting was just reward.
Yet another birdie followed before par's at 17 and 18 got him into the clubhouse at nine under - three clear of his nearest competitors.
In this form, McIlroy is all-but unbeatable and with the former U.S. Open winner out early Friday he can open up a commanding lead at the top having torn Muirfield Village apart in such fashion on the first day; it was the lowest opening round by anyone at the course for the past 39 years.
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