Rory McIlroy's woes continued in the first round of the 142nd Open Championship as the world number two slumped to an ugly opening eight-over 79 that left him 13 shots off leader Zach Johnson.

The 24-year-old, whose form has deserted him since he changed clubs at the start of the year after signing a mega-bucks deal with Nike, sported a look of sad resignation when he walked off the 18th green at Muirfield.

The scorching sun may have been beating down on the banks of the Firth of Forth but the storm clouds hovered over McIlroy's head from the start.

The nadir of an abject round came on the 15th hole, where the Holywood man putted so far past the flag that the ball travelled the full length of the green and ended up in a bunker, from where he made double-bogey.

But while the Northern Irishman toiled, Zach Johnson, who opened last year's tournament at Royal Lytham with a 65, seemed to breeze round after an eagle at the 559-yard fifth kick-started his charge up the leaderboard.

After a birdie at the third, he picked up four shots in three holes to reach the turn in 31 and a 20-foot birdie on the 12th took him to six under before handing back a stroke two holes later and then parring his way home.

By contrast, McIlroy had four sixes on his card - two of which were double bogeys.

He managed just two birdies, both at par threes, and despite claiming he had found a new driver he felt worked for him he hit just 35 percent of fairways - well below the 61 percent average for the rest of the field.

"Sometimes I feel like I am nearly walking around there and I'm unconscious" - Rory McIlroy

McIlroy - who yesterday told Nick Faldo he did not need his help after the six-time major winner publicly offered some advice - labelled himself "brain dead" for some of his shot selections in going for pins which were not really achievable.

"Sometimes I feel like I am nearly walking around there and I'm unconscious," he said.

"I can't really fathom it at the moment, it is hard to tell you what's going wrong."