Nightmare start for under fire Rory McIlroy at the British Open

World number two Rory McIlroy endured a horror start to this year's British Open, collapsing to five over par by the 12th hole, already 10 shots off the early lead held by American Zach Johnson.

While others tore up the front nine on a fast but fair Muirfield course, McIlroy struggled to the turn in one over before two consecutive bogeys followed by a double bogey on the 379-yard, par-4 12th.

It was the worst possible start for a player looking to silence those who think he is somehow distracted and not fully focused on his golf.

McIlroy struck back at his critics on Wednesday, insisting his game was "heading in the right direction" on the eve of the Open and asking "what's the big deal?" about his recent slump.

The Ulsterman has failed to win a tournament all year after changing his management company and deciding to switch equipment providers, from Titleist to Nike.

Some pundits have suggested his high-profile relationship with tennis star Caroline Wozniacki may also be contributing to his decline.

Fans are desperate for McIlroy, the youngest player to win two majors since Seve Ballesteros in 1980, to rediscover his form.

McIlroy has fended off what he regarded as unwarranted advice from major winners Nick Faldo and Tony Jacklin.

Faldo said he should focus 100 percent on golf, while Jacklin said he needed to play more tournaments.

"It seems like a few guys have forgotten in a short space of time how hard you have to work and how tough this game can be," McIlroy told a pre-tournament press conference on Wednesday.

Asked what he thought about all the criticism he was getting, the 24-year-old reigning US PGA champion replied: "What's the big deal? I haven't had the best six months, but it's okay. I'm fine. I've got a good life. So, you know, it doesn't bother me. I'm in a good place."

McIlroy did birdie the 13th but barring a miracle finish, Thursday's round was only likely to see scrutiny of his lacklustre game intensify.