DUBLIN, Ohio -- A day after cruising to a 63 and the first-round lead at the Memorial, Rory McIlroy came crashing down the leaderboard Friday with a gruesome stretch of three consecutive double-bogeys.
He said a knee injury suffered during Thursday's first round was not a factor in the high score.
McIlroy shot a 6-over 78, including a 43 on the back nine at Muirfield Village Golf Club -- his opening nine of the round. After starting at 9 under, McIlroy finished at 3-under 141, nine strokes back of leader Paul Casey.
"I missed fairways; that was the big thing," McIlroy said about the difference from Thursday. "I didn't realize how thick the rough was until I got in it today. It's thick.
"I hit a decent drive on 10 [his first hole], was just in the rough, couldn't get to the green, made bogey there. And then I just kept missing fairways and making it tough for myself. And obviously that little three-hole stretch -- 13, 14, 15 -- didn't help. Take those three holes out of it, then it wouldn't actually have been that bad a day.
"These little runs I'm getting on where it gets away from me, I was able to avoid that last week. Not so much this week."
This was the fourth straight event on the PGA Tour that McIlroy had a nine-hole score of at least 40. All occurred in the second round -- at the Masters, Wells Fargo Championship and Players Championship. In each tournament, he rallied to finish among the top 10.
Last week, McIlroy earned his first win of the year when he captured the BMW PGA Championship, the European Tour's flagship event, despite his very public breakup with tennis star Caroline Wozniacki, to whom he was engaged.
McIlroy put aside the distraction to win for the first time as a pro on European soil and move back into the top 10 in the world at No. 6. He followed it up with Thursday's 63 that included a double-bogey.
During that round, McIlroy "tweaked" his left knee on the seventh hole, and it seemed to cause him discomfort for several holes. He said afterward he would get treatment and downplayed the injury.
On Friday, however, McIlroy said he started having issues again on the driving range, but he refused to use it as an excuse for the 15-stroke differential between the two rounds.
"The knee's OK," said McIlroy, who described it as a slight MCL sprain. "It was a little sore this morning on the range because if I just keep hitting balls continuously and just keep torquing it, then it's going to get sore.
"But out on the course it was fine. Painkillers kicked in. I felt it a little bit, but it didn't really bother me too much."
McIlroy's string of doubles began on the par-4 13th hole, where three consecutive shots hit trees en route to a 6. At the 14th, which he also doubled Thursday, he found the water.
At the par-5 15th, McIlroy was actually close to the green in two shots, but his ball was near a bunker and he had a difficult chip shot that he hit twice, the ball going behind him into a bunker. He then knocked it on the green and took two putts to get in for a 7.
"Seemed like anything that could sort of go wrong did go wrong out there, with having double hit on 15 and hitting a couple of branches on 13, which were actually a couple of decent shots," McIlroy said. "Even the tee shot on 18, I felt like I had a good tee shot. Might have been a little too much club, [to] end up with a shot where I don't have a shot to get to the green."
After the bogey at 18, McIlroy went to the front side, where he had two birdies and a bogey to shoot 35.
"It's not disastrous," he said. "Even though I had such a bad day, I'm still in with a chance, depending on what the guys do this afternoon. So going into the weekend, not exactly where I want to be. But could be worse."