After snaring the first-round lead with an opening 63 at Muirfield Village Golf Club, McIlroy looked like a different player as he struggled to a six-over-par 78.
But McIlroy did not blame his dismal day on a sore left knee he tweaked during the first round, instead admitting that it was poor driving that left him three strokes behind clubhouse leader Thorbjorn Olesen.
“I just kept missing fairways and making it tough for myself and obviously that little three-hole stretch didn’t help,” the Northern Irishman said afterwards.
“Take those three holes out and it wouldn’t have been that bad a day but, these little runs I’m getting on, it just seems to get away from me.”
McIlroy was referring to the bad habit he has fallen into this year of shooting poor second rounds. In his past three PGA Tour events, he shot 77 (Masters), 76 (Wells Fargo Championship) and 74 (Players Championship) on the Friday.
McIlroy arrived at Muirfield Village fresh from winning the European Tour’s flagship BMW PGA Championship atWentworth on Sunday, just days after breaking up with his tennis-playing fiancée Caroline Wozniacki.
His double-bogey run yesterday started at his fourth hole, the par-4 13th, where his second shot from the rough hit a tree and ended up even deeper in the woods.
At the par-4 14th, his approach shot from the juicy rough hit the bank of the pond protecting the green and bounced into the hazard.
Even more shockingly, he also dropped two shots at the par-5 15th, where he hit the ball twice playing a bunker shot, incurring a penalty stroke.
World No 1 Adam Scott, who played with McIlroy, had a far steadier day, shooting 70 totrail Olesen by one stroke with half the field back in the clubhouse.
Dane Olesen mixed seven birdies with two bogeys to shoot 67 for six-under 138.
His performance was a surprise, because he has missed the cut in four of his past six events. Many of the top players in the stellar Memorial field are using the tournament as a final tune-up for the 12-15 June US Open at Pinehurst No 2.
McIlroy had made the most of ideal scoring conditions on Thursday, shrugging off the painful knee to soar three shots clear with a spectacular nine-under-par 63 in the opening round.
He recorded two eagles on his back nine to seize control of the elite PGA Tour event hosted by Jack Nicklaus. McIlroy surged up the leaderboard with a brilliant homeward nine of 31 that included a double-bogey at the 14th.
“I obviously played really well from tee to green,” McIlroy said on Thursday night after totalling only 22 putts and ending the first round three ahead of Americans Bubba Watson and Chris Kirk, and Englishman Paul Casey.
“I holed a lot of putts as well, two really good up-and-downs at the last two holes.
“It could have been evenbetter apart from that double-bogey on 14, but I am really happy.”
Asked after that first round what was wrong with his left knee, McIlroy replied: “Honestly I don’t know.
“I felt it on my second shot on [hole] seven today. I think my foot might have just got stuck in the ground a little bit and torqued my knee.
“It was painful right after I hit shots and then I sort of walked it off for the next one and it was okay, and then it would be painful again.
“I guess I put it out of my mind when I was over the golf shots.
“I’m going to go and get some treatment on it now and have a physio look at it. This is a new injury. I haven’t felt this before.”