Rory McIlroy (Getty Images)
One bad swing ended Rory McIlroy's hopes of going into his US Open title defence with a fourth US PGA Tour victory.
The 23 year old World Number Two was joint leader at the FedEx St Jude Classic in Memphis when he hooked into the middle of a lake off the final tee.
Then, by missing a four foot putt, McIlroy double-bogeyed and dropped all the way to joint seventh place.
The title went instead to American Ryder Cup player Dustin Johnson in only his second event after a back injury that kept him out of golf for over two months.
Johnson birdied two of the last three for a four under par 66 and on nine under a one stroke victory over compatriot John Merrick, whose chip to force a play-off lipped out.
"I was at home for ten weeks or something - it was tough," said Johnson, who now moves back into the world's top ten.
"Last week I was a little rusty and didn't finish off my rounds, but this week I finished a lot better."
Halfway leader McIlroy had resumed one behind Merrick, Davis Love III and Nick O'Hern, but after birdies at the second, fourth, seventh and short 11th, where he almost holed-in-one, he found himself two in front.
After three successive missed cuts it was shaping up to be the perfect comeback, but it was not to be on a day when the top of the leaderboard changed 26 times.
The Northern Irishman found water on the next and three-putted the 14th for another bogey before conjuring up a brilliant birdie at the penultimate hole.
Finding the left rough forced him to go under a tree with his approach, but he ran the ball up to 20 feet and sank the birdie putt to move alongside Johnson, Chad Campbell and Merrick.
Johnson had holed from 11 feet at the long 16th and as he followed that with an eight footer both McIlroy and Campbell both dumped their final drives into the drink.
Campbell made bogey and ended up joint third with Ryder Cup Captain Love, Ryan Palmer and Australian left-hander O'Hern, another to find the water on the last.
England's Greg Owen closed with a 65 for joint 11th, while Dubliner Padraig Harrington, Swede Henrik Stenson and Scot Martin Laird shot 69s to be 13th and 24th respectively.
The final round tee-off times had been brought forward because of the threat of bad weather.