Lee Westwood found himself leading The Masters again after Henrik Stenson crashed from six under par to one under in almost a blink of the eye at Augusta National on Thursday.
Westwood, making his 56th attempt to win a major, had four birdies in a row from the fifth and ended the day on five under one in front of South Africa's 2010 Open champion Louis Oosthuizen.
His former Ryder Cup team-mate Stenson, spectacularly good for 15 holes, followed a three-putt bogey on the short 16th with a quadruple bogey eight at the last and had to settle for a one under 71.
The Swede was not the only one to hit trouble - Rory McIlroy's return to the course started with a double bogey and was one over after 14, while Luke Donald shot 75 before being involved in a scorecard inquiry, although there was no disqualification for the world number one as it was an administrative error.
Tiger Woods bogeyed the last two holes for a 72 and reckoned he had hit some of his worst-ever drives, but Scot Paul Lawrie, playing the event for the first time since 2004, eagled the 13th and 15th for a three under 69 that had set the early clubhouse target.
Four-time champion Woods, the pre-tournament favourite after winning at Bay Hill a fortnight ago, saved par from the left-hand trees on the first two holes - he had to take a penalty drop on the long second - and holed from nine feet for birdie at the third.
A birdie at the 10th took him to two under, but he missed out on birdies at the two inward par fives. Through the green in two on the 13th he failed to get up and down from the sand, while at 15 another drive left forced him to lay up short of the water.
Despite the soft conditions and no significant wind the course was still presenting a real challenge for some - and nobody more than than Britain's first winner Sandy Lyle. The 1988 champion, now 54, went to the turn in a 10 over par 46 en route to an 86.
Fellow Scot Martin Laird shot 76 like England's Paul Casey and his compatriot Simon Dyson had a 78.
Open champion Darren Clarke, who came into the event with a groin strain, was one over after 15, but fellow Northern Irishman Graeme McDowell could do no better than 75.