Australian Jason Day hit the front late on to take control on a dramatic second day at the Masters that saw Tiger Woods squander a share of the lead and teenager Guan Tianlang penalised for slow play.
Day, the joint runner-up in 2011, shot 68 to finish six under, one clear of 53-year-old Fred Couples and Australian Marc Leishman at Augusta.
Woods, chasing a fifth Green Jacket and first since 2005, had a share of the lead with four holes to play but endured a sloppy finish for a 71 to end three under.
But the main talking point was the one-shot penalty handed to 14-year-old Chinese amateur Guan.
The Masters debutant ended with a 75 for four over and became the youngest ever player to make a cut in a major, but was in danger of missing out after being penalised for twice exceeding the 40-second time limit over shots.
"I respect the decision," he said. "This still is a wonderful experience. I enjoyed this week so far and think I did a pretty good job."
Bubba Watson looked like becoming the ninth defending champion to miss the cut at six over after 11 but he rallied to four over with a 73 and, like Guan, had to sweat on Day not birdieing 17 or 18, which would have moved the cut to three over.
However, last year's runner-up Louis Oosthuizen, reigning US Open champion Webb Simpson, 2010 US Open winner Graeme McDowell, three-time major champion Padraig Harrington, England's Ian Poulter and Scotland's Martin Laird all missed out.
Two shots behind Day were 43-year-old Argentine Angel Cabrera, the 2009 champion, who had four birdies in the last five holes for a 69, and Americans Jim Furyk (71) and Brandt Snedeker (70).
Alongside Woods were English trio Lee Westwood (71), Justin Rose (71) and David Lynn (73), with American Jason Dufner (69), Australia's 2011 co-runner-up Adam Scott (72) and South Korea's KJ Choi (71).
Rory McIlroy improved on his opening round by two shots with a 70 to edge to two under, but three-time champion Phil Mickelson struggled to a 76 for three over.
The day began overcast and blustery, with sharp showers mid-morning, but Day, playing in the last group in evening sunshine, birdied the short 16th to take the lead. He parred his way home to set the cut at four over as he bids to make Masters history for his country.
"Obviously there's a lot of pressure on my shoulders, being from Australia and no Australian has ever won the event," he said. "They have been very, very close, but I've just got to try to get that out of my mind and just plug away.
"It's all how you look at it. If you look at it as pressure, you're going to worry about it more."
Couples, the 1992 champion, birdied the last for a 71 to end alongside joint first-round leader Leishman, 29, who maintained his composure with a one-over 73 in only his second Masters after missing the cut in 2010.
Despite his advancing years Couples has become a regular fixture near the top of the Masters leaderboard and has finished sixth, 15th and 12th over the past three years.
"I did tee off Thursday with the idea of playing well," said Couples, who led at halfway with Dufner last year but shot 75, 72 at the weekend.
"I'm surprised, but I'm not going to freak out over it."
Woods, who won the last of his 14 major titles in 2008, picked up three strokes on the front nine and took a share of the lead when Leishman bogeyed the 14th to join him and Couples on five under. Day soon joined the group but Woods missed a chance to forge ahead when he laid up on the par-five 13th before missing his 10ft birdie putt.
The 37-year-old world number one had to lay up again on the long 15th after finding trouble off the tee, but his third shot hit the flag stick and bounced back into the water.
Woods went back to his original spot and conjured a deft pitch to four feet to salvage a bogey. He then found the left greenside bunker on 16 and got up-and-down but he dropped another shot on 18 to fall back.
"I was pretty annoyed," said Woods in reference to his third shot at 15. "It looked like I was making birdie and then I had to struggle not to drop two shots.
"It was a good six but I played really well today and the round should have been in the 60s."
The 23-year-old McIlroy bogeyed the first and third but an eagle at the eighth took him to the turn in 36 and he made three birdies and a bogey coming home.
"Anything under par today was going to be a good score and I stayed patient out there when I needed to and it was a good day," said the world number two.
"The improvement in the putting from last night to today has been a big thing."
Sergio Garcia, who shared the first-round lead, fell back after a 76 dropped him to two under. In the same group was 55-year-old Bernhard Langer, who won the Masters in 1985 and 1993 but hasn't made the cut since 2005.
England's Luke Donald carded a level-par 72 to end one under in a group that included American Dustin Johnson, who led on his own at seven under after 13 but dropped six shots in his next five holes, including two double bogeys.
Scotland's Sandy Lyle, 25 years after winning the Green Jacket, also ended one under after rounds of 73 and 72.