St Andrews: "What a difference a day makes" seemed to be the look on Rory McIlroy's face after he followed his opening course-record 63 with an ugly 80 on Friday at the British Open.

"I haven't really experienced that before," the 21-year-old Northern Irishman told a scrum of reporters eager to find out what went wrong on the Old Course after his dazzling display a day earlier.

"I two-putted for a good 80," added the world number nine, his spirits remarkably high after a trying day when most of the field were blown away by high winds of up to 64 kilometres per hour.

"I did well to par the last three holes if I'm totally honest," said McIlroy after finishing on one-under 143, a distant 11 shots behind leader Louis Oosthuizen of South Africa.

"I just let it get away from me a little bit. It could have been an 82 or an 83. I was starting to get very frustrated."

McIlroy's confident swagger of Thursday seemed a distant memory as his ball repeatedly failed to obey his commands, sapping the confidence out of the talented youngster.

On 18, having driven near the green, he trudged disconsolately after his ball when it rolled back into the unforgiving "Valley of Sin" following his second shot.

"I'm here for the weekend so it's not all bad. I'm just going to go back now and have a bit of room service and get some sleep and get ready for tomorrow," he said.

"If you take Louis and Calc [Mark Calcavecchia on seven under] out of it I'm only five shots out. It depends what the weather does tomorrow.

"If the weather is quite calm I feel as if I've got a chance to go low. But when it's wind like this, you're relying on other players to make mistakes," added McIlroy.