|McIlroy's compatriot Colm Moriarty shared the joint lead after the first round of the Irish Open [GALLO/GETTY]
Rory McIlroy's hopes of victory in the Irish Open sank with his ball at the 18th during his opening round at Killarney on Thursday.
The U.S. Open Champion dismayed a huge adoring gallery when he dunked his ball into the water at the 18th hole to run up a double-bogey six in the Irish Open first round.
The 22-year-old local hero said rustiness was the likely cause as he posted a one-under 70 that left him three shots behind the early pacesetters.
"I think I was probably rusty," said McIlroy who has played little golf since finishing tied 25th in the British Open two weeks ago.
"I was caught in two minds with a few shots, which isn't like me, and was not very decisive off the tee," the world number four told reporters.
In a twitter
McIlroy later shared a bitter exchange on Twitter with American Jay Townsend, a former European Tour player who now works for BBC radio.
Townsend tweeted: "McIlroy's course management was shocking. Some of the worst course management I have ever seen beyond under-10 boys' golf competition."
McIlroy quickly replied: "Shut up ... you're a commentator and a failed golfer, your opinion means nothing!"
His six at the 18th came when he tried to reach the green from sand.
"Fairway bunker play wouldn't be one of the strongest parts of my game," the Northern Irishman told reporters.
"Shut up ... you're a commentator and a failed golfer, your opinion means nothing!"
McIlroy lets loose on Twitter
Earlier, McIlroy played a stroke which he placed in his all-time top five, bending his ball around trees and on to the green at the 14th after having produced another erratic tee shot.
It was not the best of mornings either for 2010 U.S. Open champion Graeme McDowell (72).
One Northern Irishman was going well, though. Colm Moriarty claimed an early share of the lead on 67 with a group which also included defending champion Ross Fisher of Britain, Australian Richard Green and Dane Soren Hansen.
The other two players attracting a huge crowd at Killarney, British Open champion Darren Clarke and three-times major winner Padraig Harrington started poorly in the afternoon with early bogeys.