Charlotte - Three-time Masters champion Phil Mickelson fired a five-under par 67 on Friday to seize a two-stroke lead after the second round of the $6.7m US PGA Wells Fargo Championship.
US left-hander Mickelson, who opened with a 14-foot birdie putt on his way to back-to-back birdies, stood on nine-under 135 after 36 holes at Quail Hollow.
"I got off to a good start so that set a good tone for the round," Mickelson said. "I really am excited about the way I'm hitting it off the tee. If I drive it well this weekend, it's going to be a fun weekend. And I fully expect to."
Australia's Scott Gardiner, who fired a bogey-free 67, shared second on 137 with Americans Nick Watney and George McNeill with world number two Rory McIlroy among five others sharing fifth place, three strokes off the pace.
Mickelson also birdied the par-5 seventh and the ninth before taking his lone bogey at the 12th, which he answered with birdies at the 14th and par-5 15th to move atop the leaderboard by himself.
"I have to drive it better to be more aggressive to shoot lower this weekend because I'm getting as much out of the round as I can," he said.
Mickelson, who finished second behind McIlroy at Quail Hollow in 2010, likes his chances to win an elusive first US Open title after five runner-up efforts next month at Merion.
"I would love nothing more than to win a US Open," Mickelson said. "Finishing second five times and not ever winning it would be a huge disappointment and I think Merion is going to be a good opportunity for me because it's not necessary to hit drivers off a lot of holes.
"And the strength of my game, which is short mid-irons into the green, I think that will give me a good chance."
Northern Ireland's McIlroy was on 138 after a second-round 71. He began and ended the back nine, his first nine holes of the day, with bogeys, but responded with birdies at the first and fourth and made another at the eighth.
That left McIlroy, one of seven co-leaders after day one, level with England's Lee Westwood, Australian Rod Pampling and Americans Jason Kokrak and Derek Ernst.
"I hit the ball really well again and gave myself a lot of opportunities," McIlroy said. "I actually played pretty well on the back side. I gave myself plenty of chances. I just didn't take any of them.
"It took me a while to get adjusted to the green speeds this morning. They were a lot quicker than they were last night. I misjudged my first putt on 10. I had a 15-footer for birdie and hit it 10 feet past so that was a nice little wake-up call."
McIlroy, in his first event since sharing 25th at the Masters, has big expectations for the next few months, including a title defence at the PGA Championship in August at Oak Hill as well as next month's US Open and the British Open in July.
"I'm comfortable with my game," McIlroy said. "I feel good. I'm looking forward to a big summer coming up."
Gardiner put himself in the final pairing with a sizzling start, opening with a birdie and then adding four in a row to conclude the front nine, the last a seven-foot birdie putt before missing a 16-foot birdie bid at the 10th.
"Probably nobody is more surprised than I am," Gardiner said. "I just haven't been putting it together. I've putted poorly all year, haven't really saved any shots around the greens.
"It's just nice to get a few birdies and save a few pars because when I have been giving myself opportunities I haven't been taking them."
Gardiner, of Aborignal heritage, received a boost as a young golfer from a program called "The Hunt for the Australian Tiger" in 2000 when Tiger Woods was the sport's brightest star.
"Coming into turning professional I was afforded some scholarships... which sort of helped take me from a good amateur to starting a professional career."
Leading second-round scores on Friday from the US PGA $6.7m Wells Fargo Championship at Quail Hollow (USA unless noted, par-72):
135 - Phil Mickelson 68-67
137 - Scott Gardiner (AUS) 70-67, Nick Watney 67-70, George McNeill 69-68
138 - Rory McIlroy (NIR) 67-71, Lee Westwood (ENG) 70-68, Rod Pampling (AUS) 69-69, Jason Kokrak 68-70, Derek Ernst 67-71
139 - Lucas Glover 68-71, David Lynn (ENG) 71-68, Robert Garrigus 67-72
140 - DA Points 71-69, Kevin Streelman 68-72, Russell Henley 69-71, Zach Johnson 68-72, Brian Harman 70-70, Daniel Summerhays 67-73, Sergio Garcia (ESP) 72-68, Jordan Spieth 69-71
141 - Ted Potter 71-70, Ross Fisher (ENG) 70-71, Nate Smith 67-74, David Hearn (CAN) 69-72, Robert Karlson (SWE) 69-72
142 - Dicky Pride 71-71, Angel Cabrera (ARG) 73-69, Kyle Stanley 74-68, Stuart Appleby (AUS) 71-71, Vaughn Taylor 70-72, Shawn Stefani 69-73, Ryan Moore 67-75, Trevor Immelman (RSA) 70-72, James Driscoll 70-72