DUBLIN, Ohio (AP) -- Rory McIlroy hit into the water and into the trees. He even hit one shot twice.
Instead of seizing control Friday in the Memorial, he was 15 shots worse than his opening round and tumbled down the leaderboard at Muirfield Village.
McIlroy had to scramble for par on his final hole for a 6-over 78, turning a three-shot lead into a three-shot deficit among early starters in the second round.
Thorbjorn Olesen of Denmark had a 67 and was the clubhouse leader at 6-under 138.
McIlroy said the left knee he hurt on Thursday caused some pain on the driving range as he hit one ball after another. He said it didn't bother him on the golf course. The bigger problem was getting the ball in play. He didn't hit a fairway until his eighth hole (No. 17) and hit only four fairways.
"I didn't realize how thick the rough was until I got in it today," McIlroy said.
Olesen used the recipe that carried McIlroy in the first round -- he found the fairway and holed putts, which works for everyone at Muirfield Village.
Adam Scott, who won Colonial last week in his debut at No. 1 in the world, kept it together with a 70 and was among those one shot behind. Jordan Spieth scrambled to a 72 in a round that could have been higher and was tied with McIlroy at 3-under 141.
Phil Mickelson finished a little bit better in his round of 70 and was still in the mix at 142.
McIlroy, a winner last week at Wentworth in the BMW PGA Championship, has been happy with his game except for the odd stretch of big numbers. That came back to haunt him again Friday in an ugly back nine that continued a most peculiar trend.
Starting his round on No. 10, he shot 43 on the back nine. It was his fourth straight PGA Tour event, and fifth out of his last six U.S. events, that he had a 40 or higher over nine holes. All of them have come in the second round.
It started to unravel on the par-4 13th when McIlroy hit a tree trying to get out of the rough and clipped another tree in a futile attempt to find short grass. He made double bogey. He missed the fairway with an iron off the 14th tee and hit his next shot into the water and made another double bogey.
And on the par-5 15th, he was just left of the green in two when he hit a flop shot out of thick rough near a bunker. He hit the ball twice, and it tumbled back into the bunker, leading to a third straight double bogey.
McIlroy played 1 under on the front nine to keep in the game.
"These little runs I'm getting on where it gets away from me, I was able to avoid that last week," McIlroy said. "Not so much this week. But it's not disastrous. 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 it could be worse."
Mickelson dropped five shots over his last three holes on Thursday for a 72. He ran off three birdies in four holes on the front nine. But he failed to birdie either of the par 5s, taking a three-putt par from 18 feet on the seventh hole, and he hooked his tee shot into the bunker on No. 8 for a bogey.
He was four shots behind Olesen among the early starters.
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