Second round leaderboard:
-9 B Mayfair (US) -7 D Love III (US) P Mickelson (US) -6 JJ Henry (US), D Johnson (US), A Cabrera (Arg) -5 R McIlroy (NI)
Selected others: -2 P Harrington (Ire) R Fisher (Eng) Level L Westwood, G Owen (both Eng)
McIlroy has endured a recent slump in form
Northern Ireland's Rory McIlroy shot a third round six-under-par 66 to surge into contention at the Quail Hollow Championship in North Carolina.
McIlroy missed the cut in his last two events in the United States but looked back to his best in a round containing nine birdies and three bogeys.
The 20-year-old, who turns 21 on Tuesday, is on five under with American Billy Mayfair leading on nine under.
"A 66 is a great score and puts me in a nice position," McIlroy said.
"It was a great round of golf, I played really, really well.
"I feel as if I've been hitting it well the last couple of weeks and not getting much out of it but today I knocked a few putts in and gave myself plenty of chances.
"I'm just happy to be where I'm at because the last couple of months have been a struggle."
Asked to explain what has turned his game around, McIlroy added: "I've had to put a lot of work in.
"I had a little bit of a back injury. It's still there but getting a lot better and I feel I can swing with a lot more freedom now and actually practice more and spend a bit more time on the range which has definitely helped.
"I put my old trusty putter back in the bag on Friday night which helped, my pace was pretty good out there today. Hopefully I can do the same on Sunday."
American duo Davis Love III and Phil Mickelson are Mayfair's closest challengers on seven under with another US pair, JJ Henry and Dustin Johnson, and Argentine Angel Cabrera a further shot behind the leader.
Masters champion Mickelson admitted he was off his game but was pleased to have limited the damage in his round of 71.
"I didn't have it today," he said. "I didn't have great control over my ball-striking and missed a number of putts that I probably could have made.
"But I controlled the misses, kept the round in check and because of the difficult conditions was able to shoot a number that kept me in contention for Sunday, so I'm excited about my opportunity."
England's Ross Fisher shot a 69 to take him to two under and a share of 26th, where he is joined by Ireland's Padraig Harrington, who carded a third-round 70.
Further down the leaderboard, in a tie for 42nd is Englishman Lee Westwood, who went to one under with a round of 71 on Saturday.