Rory McIlroy and Sergio Garcia moved into a share of the Masters Tournament lead as Lee Westwood paid the price for a closing double bogey at Augusta National.
England's World Number Three, ahead by one after an opening 67, still held that advantage until he missed the 18th green, chipped ten feet past and ran up a six.
A one over par 73 dropped him to four under for the opening Major of the season and out in front on five under instead were McIlroy, who still had two to play, Spanish star Garcia and Americans Jason Dufner and Fred Couples - champion 20 years ago and now 52.
McIlroy, of course, was back in the position he held with nine to play a year ago, prior to the final round 80 that saw him finish behind Charl Schwartzel.
Westwood reeled off ten pars in a row, then responded well to dropping his first stroke on the difficult 11th.
He holed from eight feet at the 155 yard next, then escaped with a par on the long 13th after his second shot headed towards Rae's Creek, but did not go into the water.
The 38 year old was on the back of the green in two on the 530 yard 15th and two-putted before being left to rue his disappointing finish.
McIlroy, who began the tournament with a double bogey, birdied the third, fourth and seventh.
He three-putted the tenth but was on in two at the 13th and after two-putting for birdie there added another on the 15th.
He missed the green to the right there, but chipped over the bunker to nine feet and made it.
Westwood said: "It was a disappointing way to finish, but if you get out of position on this course it can punish you.
"These things happen and they will happen to everybody."
Henrik Stenson was leading when he took eight on the hole on Thursday.
"I thought I made a few putts that didn't drop," added Westwood. "But I'm right in there for the weekend and that's where I want to be.
"The greens are getting more fiery and the wind is making it tricky."
He also had to contend with much cooler conditions earlier in the day.
Dufner had bogeyed the last for a 70, but Couples, who was sixth only two years ago, parred it for a brilliant 67 and became the second player in the clubhouse on five under.
Garcia needed to par the last to match Couples' 67, but he fired his approach into the crowd and bogeyed to be four under with Oosthuizen, Westwood and also McIlroy, who could not get up and down from sand at the 17th.
