Lee Westwood's patience paid off as he sank three birdies in a row to rescue his second round and take a share of the halfway lead at the St Jude Classic in Memphis.
Overnight leader Westwood had been struggling to repeat his impressive opening-day form at a gusty TPC Southwind.
The World Number Three, still looking for his first win in the United States since 1998, shot a course-record 63 to lead the US PGA Tour event after round one on seven under par, but the Englishman had been one over for his second round after 14 holes, having undone an early birdie with bogeys at the eighth and 14th.
Then came Westwood's rally, a hat-trick of birdies on 16, 17 and 18 giving him a 68 and leaving him at nine under after 36 holes.
"It was tricky out there this afternoon," Westwood said. "The wind got up and it was gusty, so quite hard to judge.
"It was a day of patience. I didn't hit the fairways early on, so I was coming out of the rough a lot. I wasn't missing the fairways by a long way, just on the edge.
"You've got to be on the fairway to attack the flags, and I just didn't hit it close enough to the flag early on.
"So it was a day of patience and battling, and I was rewarded at the end of the round with three birdies for doing that."
Westwood will now head into the weekend as joint leader with American Garrett Willis, who shot a 65, one shot clear of another American, Charley Hoffman, who also carded a five under round at the par 70 course.
"When I bogeyed 14, I stood on the 15th tee and set myself a little task of trying to birdie two of the last four holes to shoot under 70," added Westwood.
"I birdied the last three holes, and I had a chance at 15, too. I'm pleased with that. It's a great way to finish off the day. It sends you into tomorrow with momentum.
One stroke behind Hoffman was Sweden's Robert Karlsson, a European Tour winner this year in Qatar having spent more than four months out last season with an eye problem. He followed his opening 67 with a four under 66 and was delighted with his day's work.
"I'm very, very happy with where I'm standing," Karlsson said. "I took the last couple of weeks off, practised last week and came here to get going after practising, because it's quite difficult if you work a bit on your swing and things like that to get into tournament mode again.
"That was the most important thing for my getting here. It's beautiful golf course. It's a good test. It's great to be here."
Northern Ireland's McIlroy, the World Number Ten, was bogey free for the second day in a row but he improved by three shots on his opening 69 to get to five under and into a tie for tenth.
Ireland's Padraig Harrington, though, had a less successful day. The three-time major winner followed his opening 65 with a second round 74 to slip down the leaderboard to one under par, alongside Sweden's Fredrik Jacobson (70), while Retief Goosen of South Africa was among those a shot back on level par after a 68.
