Chad Campbell fired six birdies in a five-under 67 to take a three-shot lead at the halfway stage of the Masters.
US unless stated
-6 Chad Campbell
-3 Rocco Mediate, Vijay Singh (Fij), Fred Couples
-2 Darren Clarke (NIre), Phil Mickelson, Ernie Els (SA), Tim Clark (SA), David Howell (Eng)
-1 Nick O'Hern (Aus), Billy Mayfair, Padraig Harrington (Ire), Olin Browne, Ben Crenshaw, Retief Goosen (SA), Tiger Woods
The 31-year-old American matched the best round of the week to improve his score to six under par.
Tied for second behind Campbell are Americans Rocco Mediate and Fred Couples and Fiji's Vijay Singh.
One further back are British pair Darren Clarke and David Howell, American Phil Mickelson and South African duo Ernie Els and Tim Clark.
World number one and defending champion Tiger Woods and world number three Retief Goosen are five off the lead on one under.
Singh, the overnight leader, had an eventful day that could have been a lot worse. He mixed five birdies, with three double-bogeys and a bogey.
"I'm happy I hung in there," said Singh, the 2000 champion. "You can't win the tournament today."
Northern Ireland's Clarke birdied the last to post a two-under 70, while world number four and 2004 champion Mickelson bogeyed the last for an even-par 72.
"I left some shots out there," said Mickelson. "But the way I look at it, I'm in good position.
"It was a day that was tough, so to be within striking distance, I'm excited about that and looking forward to the weekend."
Els, ranked fifth in the world and runner-up here twice, was four under through eight but a double at 10 and another bogey at 12 reined him back.
"If you shoot anything like I've shot the first two days on the next two days, I think you will be right in there," Els said.
"Two under seems like it's not too bad. Conditions are getting tougher out there. I'll take what I've got.
"I've just got to try to sneak something into the 60s this weekend and see what happens. I know you don't have to try to shoot 65."
His South African compatriot Clark birdied four straight from 12 but dropped a shot at the 17th to slide back to two under.
Like his Ryder Cup team-mate Clarke, England's Howell finished with a birdie for his second straight 71. The in-form 30-year-old is two under for the tournament.
Others to post good scores were Australian Nick O'Hern and Americans Billy Mayfair and Olin Browne, all now on one under.
Alongside them is Ireland's Padraig Harrington, who fired a two-under 70 in his second round.
And the 54-year-old Ben Crenshaw continued his remarkable progress with a 72. The two-time champion, who has missed his last eight cuts at Augusta, is also one under.
"This has always been my favourite place," said Crenshaw. "For six or seven years, I didn't play worth a darn."
Campbell, who won his third career PGA Tour title in January, fired three straight birdies from the 12th, bogeyed the 17th but then finished with another birdie at 18.
Campbell, who made his Ryder Cup debut two years ago and is playing his fourth Masters, said: "It's nice to see the ball rolling because the course is not playing as long as I thought it would be.
"It's definitely playing tough, though. It's nice to be leading after two rounds, but the goal is to be leading after four.
"This is a special place and a special tournament. I'm glad to be a part of it and glad to be playing well. It's a good start. I like where I'm at."
Australian Mark Hensby was the other player to card a 67 on Friday, but unlike Campbell he was starting on eight over after his first-round 80.
The vastly improved showing, however, was enough for Hensby to make the weekend which was beyond a number of big-name players.
Among those who missed out were Britain's former champions Nick Faldo, Sandy Lyle and Ian Woosnam, Germany's two-time winner Bernhard Langer, US Open champion Michael Campbell, last year's runner-up Chris DiMarco, eight-time European number one Colin Montgomerie and British Amateur champion Brian McElhinney.