Rory McIlroy has blamed his inability to adjust to the unique Olympic Club course for his US Open exit.
The defending champion missed the cut by two shots at the halfway stage in San Francisco.
McIlroy, 23, ended the tournament on 10-over following a first round of 79 and a second round of 73.
"It's just such a demanding golf course and punishes the slightest shot that's off-line or that's maybe not the right distance," said McIlroy.
"You really have to be so precise out there and if you're not, you're going to get punished. We're just not used to playing this sort of golf course week in, week out.
"We're not used to having to land balls before the edge of the greens to let them run on. It's just something that you have to adjust to in this tournament. I wasn't able to do that very well this week."
Aside from joint-leaders Tiger Woods, Jim Furyk and David Toms, no other player is currently under par on the leader board.
