Gullane, United Kingdom: Rory McIlroy and Justin Rose both made nightmare starts to the British Open at mighty Muirfield on Thursday as US wedge-king Zach Johnson set the early pace with a 66.

World number two McIlroy, desperately seeking the form that has eluded him since he changed clubs at the start of the year, had two double bogeys down the back nine en route to a morale-sapping eight over 79.

The lowest point of his round came at the 15th, where he shook his head in disbelief after watching his long putt speed over the rock-hard green and bury itself in a deep pot bunker.

A second double-bogey was the end result of that and he looked a disconsolate figure trudging off the 18th green with the question mark over his current form beginning to take on giant proportions.

“I sort of hung in there. I made sloppy bogeys on four and five, then a good birdie on seven. I let shots get away from me — too many loose shots,” the 24-year-old McIlroy said.

“Silly mental errors cost me. I missed the ball in wrong places — you can’t do that with the firmness of the greens.

“I made stupid mental errors. It’s got so fast and firm. If you’re not in total control of the golf ball it’ll be quite difficult.”

Last month’s US Open winner Rose needed 17 holes before bagging his only birdie of the day and a double-bogey and three bogeys meant that he came in with a disappointing 75.

Both McIlroy and Rose failed to deal with the exceptional conditions at Muirfield, where two weeks of pure Scottish sunshine had left the famed links course running fast and furious.

More blue skies and temperatures nudging 80 degrees Fahreinheit (26 Celsius) on Thursday made the greens treacherous and at times Augusta National fast, especially around the pins.

Johnson, whose sole win in a major came at the 2007 Masters, where his exceptional wedge play was the key, eagled the par-five fifth to set him on his way to a tremendous five-under 66.

A shot further back came rising Spanish star Rafael Cabrera-Bello, with three players grouped on 68 — Spanish veteran Miguel Angel Jimenez and American sharp-shooters Dustin Johnson and Brandt Snedeker.

Todd Hamilton, who upset the odds to win the 2004 Open at Troon, was on 69 and he was joined there by Angel Cabrera of Argentina, and four-time major winner Phil Mickelson, who won last week’s Scottish Open

“I love the fact that I shot under par, because it’s a very challenging course out there. I don’t expect anybody to beat the lead from the morning wave, I just don’t think it’s possible,” said Mickelson.

Nick Faldo’s return to Muirfield, where he won the Open twice, failed to find a spark as he struggled to a 78, while “golden oldie” playing partners Tom Watson and Freddie Couples also found it tough going with a pair of 75s.

“The golf course is tough, you know. It’s hard work. It’s like glass now,” said the semi-retired Faldo, who was celebrating his 56th birthday.

Tournament favourite Tiger Woods set off in mid-afternoon in the company of two other fancied players and major winners, Graeme McDowell and Louis Oosthuizen.

Also out later and playing together were Masters champion Adam Scott of Australia, England’s former world number one Luke Donald and American world number six Matt Kuchar of the United States.