By Mark Lamport-Stokes
AUGUSTA, Georgia (Reuters) - Former British Open champion Louis Oosthuizen grabbed an early one-shot lead on a day of high drama and tumultuous swings of fortune in the opening round of the Masters on Thursday.
The South African holed a 20-foot birdie putt at the tricky par-four last for a four-under-par 68 while British world number one Luke Donald was being investigated by tournament officials over suggestions he had signed for the wrong score.
While Donald's plight was in the balance, 2010 British Open champion Oosthuizen was delighted to take control of the year's opening major with four birdies in the last five holes.
"It was a really good round," the 29-year-old said after covering the back nine in three-under 33. "It was probably a bit bumpy in the beginning, but I kept going. This golf course, you've got to be very patient.
"I played really well at the end, hit a lot of fairways, hit it pretty close (with approach shots) and made a few putts."
Oosthuizen tamed the tricky 18th in the opening round but the hole took a brutal toll on the players as Tiger Woods and Henrik Stenson both came unstuck there.
Tournament favorite Woods bogeyed the hole after driving well left into the pine trees and Swede Stenson, who had led the field by two shots standing on the 18th tee, wound up with an ugly quadruple-bogey eight.
Woods finished with a level-par 72 to lie four strokes behind Oosthuizen, and three adrift of Britain's Paul Lawrie, Spaniard Miguel Angel Jimenez, Italy's Francesco Molinari and American Ben Crane.
Stenson, who had eagled the second and eighth to briefly lead the field by two, returned a 71.
Heavy rain on the eve of the tournament had softened the severely contoured layout and organizers, in response, set up several very tough pin positions to give the course extra bite for the first round.
"I hit some of the worst golf shots I've ever hit today," four-times Masters champion Woods said after offsetting three birdies with three bogey. "I squeezed a lot out of that round.
"I just hung in there and grinded my way around the golf course and stayed very patient, stayed in the moment. I could have shot one, maybe two better, but I got a lot out of that round.
"It's brutal out there, it's very, very tough. Some of these pins, like that pin on five, we haven't seen that in a while. The majority of the pins were tough."
Woods bogeyed the last two holes as the shifting breezes intensified at Augusta National after a sun-splashed morning of relative calm.
Former British Open champion Lawrie was among the early starters and he took advantage, eagling the par-five 13th and par-five 15th on the way to a three-under-par 69.
"The greens are in fantastic condition and rolling pretty well," Lawrie said after covering the back nine in four-under 32. "This course is all about the speed and patience and I struggled with that on the front nine but then I got into it in the back nine."
A bogey at the 14th was followed by a birdie on 15 before the Swede again faltered at the 16th.
The Swede, who celebrated his 36th birthday on Thursday, then limped to the finish with his nightmarish eight at the last which began with a wayward drive into the trees and ended with a missed three-foot putt.
U.S. Open champion Rory McIlroy, who squandered a four-shot lead going into the final round here last year, was one over after 13 holes and three-times Masters winner Phil Mickelson was four over after 12.
(Editing by Frank Pingue)