Bradley, the 2011 PGA Champion, moved to 13-under for the $7 million tournament at Kuala Lumpur Golf and Country Club, overtaking first-round leader and fellow American Ryan Moore.
Bradley said he was having a blast playing "some of the best golf I've played in a long time".
"I'm in a great spot with two rounds to go. Every hole out there you can make a bogey. There is no easy hole," said Bradley, ranked 15th in the world.
"I got to keep playing aggressively and shoot a good round the next two days."
Bradley fired in seven birdies, including five on a torrid final nine.
"I'm very excited with the way I'm hitting the golf ball and when I'm hitting like this and my putter matches up, normally I'm going to be right in there contending for the tournament, and that is the case here," he said.
Moore was second at 9-under after he followed up his sizzling opening-round 63 with an even-par 72.
Thailand's Kiradech Aphibarnrat and Chris Stroud of the United States were tied for third at 8-under, with Spanish star Sergio Garcia lurking one stroke back.
A day after complaining that he played some of his worst recent golf in round one, world number-three and reigning British Open champ Mickelson said he was "not much better today" as he carded a two-under 70.
That left him 10 shots off the pace and tied for 24th at 3-under.
"I don't have control of the swing," he said.
"You need to be in control in this golf course as the rough here is very tough."
"My rhythm is better, but technically, there are still many issues to address. It's going to be tough this week and next and I will probably focus on fixing (the swing) in the off-season."
Just about the only regret for Bradley -- who spent some of his youth in Boston -- was being unable to follow his beloved Red Sox in the World Series.
Due to the 12-hour time difference, the baseball championships in Boston have been held the past two days just as Bradley was on the course.
"It's tough we don't get to watch. I know they replay it later, but in the back of my mind I was wondering what was going on," he said.
Mickelson, Bradley, Garcia and South Africa's Ernie Els are heading a bumper field at the CIMB Classic, which this year becomes the first PGA Tour event in Asia to offer points for the FedExCup championship that culminates each year in September.Leading scores after the second-round of the $7 million CIMB Classic PGA tournament at the Kuala Lumpur Golf and Country Club on Friday:
131: Keegan Bradley (USA) 65-66
135: Ryan Moore (USA) 63-72
136: Kiradech Aphibarnat (THA) 67-69, Chris Stroud (USA) 67-69
137: Sergio Garcia (ESP) 66-71, Marc Leishman (AUS) 72-65
138: Martin Laird (SCO) 68-70, Harris English (USA) 71-67, Chris Kirk (USA) 67-71, Stewart Cink (USA) 70-68, Gary Woodland (USA) 68-70, Hideki Matsuyama (JPN) 70-68
139: Bill Haas (USA) 72-67, Wade Ormsby (AUS) 70-69, KJ Choi (KOR) 68-71, Graham Delaet (CAN) 72-67, Shiv Kapur (IND) 69-70
140: Aaron Baddeley (AUS) 73-67, Josh Teater (USA) 74-66, Jerry Kelly (USA) 71-69, Jeff Overton (USA) 73-67, Kyle Stanley (USA) 73-67, Kevin Stadler (USA) 71-69, Nicolas Thompson (USA) 69-71
141: Charles Howell III (USA) 69-72, Phil Mickelson (USA) 71-70, Boo Weekley (USA) 67-74, Tim Clark (RSA) 72-69, Charley Hoffman (USA) 69-72, Billy Horschel (USA) 72-69, Rory Sabbatini (RSA) 67-74, Camilo Villegas (COL) 70-71