K J Choi took over at the top of The Masters Tournament leaderboard as three bogeys in four holes dealt a severe blow to Phil Mickelson's hopes of a fourth title at Augusta National.
Already five behind Rory McIlroy and Alvaro Quiros after an opening two under par 70, the defending champion drew closer by two-putting the long second for birdie.
But Mickelson then missed the green at the third, fifth and sixth and failed to get up and down all three times.
He was back down to level par, joint 31st and eight adrift of new leader Choi on a morning that saw two Koreans take it in turns to set the pace.
First 2009 US PGA Championship winner Y E Yang, Asia's only Major Champion so far, reached eight under, but as he bogeyed the ninth and tenth Choi - third in 2004 and fourth last April - birdied the second, fourth and short sixth.
He was eight under as a result and one in front of 21 year old McIlroy, who like Tiger Woods on one under had yet to tee off again, and two in front of Yang, American Ricky Barnes and also big-hitting Spaniard Quiros, who after his opening 65 resumed with a bogey five and followed with four pars in a row.
Luke Donald, three over after ten holes of his first round, made it all the way to three under when he followed a birdie-eagle-birdie burst on Thursday with three more birdies in the first five.
But the World Golf Championships - Accenture Match Play winner, carrying the curse of victory in the Wednesday par three competition, then bogeyed the seventh and ninth.
Ian Poulter, who in contrast to Donald dropped four shots in the last four to begin with a 74, set off again with a hat-trick of birdies - the first of them courtesy of a 40 foot putt - but bogeyed the fifth, eighth and tenth to return to two over.
Paul Casey's two-putt birdie at the 575 yard second took him to three under, but he bogeyed the fourth and seventh before getting one of them back at the uphill 570 yard eighth, where he was over the green in two almost unbelievably.
Fellow Englishman Ross Fisher, who produced a 69 in the opening group of the championship, moved joint sixth with a birdie at the third.
Former winner Sandy Lyle had an amazing start when he followed a double bogey six at the first with the first eagle of the week on the next.
Mickelson repaired some of the damage with birdies at the seventh and eighth, first curling in an approach to within a foot of the flag and then hitting a wood off pine straw onto the green at the long eighth.
A par on the next meant he turned in a level par 36 and at two under his deficit was still six with Choi having three pars in a row for an outward 33 and being joined when Quiros matched Mickelson's two birdies.
McIlroy parred the first and was third on his own one behind, while Fisher bogeyed the sixth, but got the shot back two holes later to be tied for seventh.
Poulter was level par coming up the last, Donald two under with six to go and Casey three under after he birdied the tough 11th.
McIlroy birdied the reachable second as the wind started to pick up and led on his own at eight under when Choi bogeyed the 11th and Quiros three-putted from just off the back of the ninth green.
After three bogeys in four holes Mickelson made it three birdies in four with a three at the tenth and on three under had advanced to 16th spot.
Poulter made a ten foot birdie putt on the last and although a one under halfway total was far from his goal at the start of the week the closing three could prove to be vital when it comes to the cut.
"I was really disappointed with the finish yesterday," he said after his 69. "I'm not happy. I played pretty flawless, but I had three dropped shots through unforced errors."
Donald was once more coming strong on the back nine, birdies at the 11th, 13th and 14th lifting him to four under and alongside Fisher in seventh spot, while Casey was one further back.
