DUBLIN, Ohio — Whether it’s his health or his personal life, Rory McIlroy is not easily distracted when he’s on top of his game.

McIlroy made two eagles and three birdies on the back nine at Muirfield Village — along with a double bogey — on his way to a 9-under-par 63 and a three-shot lead Thursday after the opening round of the Memorial.

A week ago, McIlroy began his week at Wentworth by announcing he and tennis star Caroline Wozniacki had broken off their engagement. Then, he went out and won the BMW Championship for his strongest win in more than two years.

At the Memorial, McIlroy caught his spikes in the turf on his second shot at the seventh hole and felt pain the rest of the round, especially when he had to put a little extra pop into tee shots or long irons. He was limping when he walked off the stage after talking about how he made five birdies and two eagles after hurting his knee.

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It was the lowest opening round in 39 years at the Memorial.

Masters champion Bubba Watson, Chris Kirk and Paul Casey each had a 66 while playing in calmer and slightly softer morning conditions. Keegan Bradley was at 67, notable not because it was his best score at Muirfield Village but because it was his first time in his four years on the PGA Tour that he did not use a belly putter.

Adam Scott, who won at Colonial last week in his debut at No. 1 in the world, settled for a 69.

Ryan Moore from Puyallup shot a 68. Michael Putnam from University Place had a 71. Kyle Stanley from Gig Harbor shot a 74. Former Husky Richard H. Lee had a 76.