Rory McIlroy has a telling quote explaining just how mentally challenging this year's US Open will be

The U.S. Open tees off on Thursday from the exceedingly challenging Oakmont Country Club, where even-par scores will be hard to come by for the world’s best golfers.

Phil Mickelson has called Oakmont the hardest course he’s ever played. Sam Snead once joked that the greens are so fast his ball-marker slid off the green. The last time Oakmont hosted the U.S. Open, in 2007, Angel Cabrera won with a four-day score of 5-over.

Speaking to the press following a practice round on Tuesday, world no. 3 Rory McIlroy gave a revealing answer to the mental challenge Oakmont forces on its golfers. Unlike leading into other events, where golfers typically express their excitement to attack a course and try to post a low number, McIlroy spoke honestly and described his nervousness.

“Trepidation,” McIlroy said when asked how he felt on the eve of the event. “It really depends the venue that you play a U.S. Open at, as well. But yeah, this week it’s definitely not excitement. You know you’re going to be put under a lot of pressure on basically every single golf shot you hit out there. So you have to be prepared for that. You have to be prepared for how mentally demanding it’s going to be, how much concentration you’re going to need out there.”

He continued: “It’s the toughest test in golf, and you know that. You have to do everything you can to prepare for that and try to do your best.”

Typically an aggressive golfer, McIlroy said that at Oakmont he’s preparing to take a more conservative, plotting approach.

“You just have to be so disciplined. I’m an aggressive player as well. So there’s just going to be times where I’m going to have to rein it back a little bit,” McIlroy said.

He also stressed that mental composure would make a difference, knowing the course is bound to frustrate.

“Mentally, that’s what’s going to win it for you this week, is how people can keep their calm and keep their composure.”

Rory McIlroy OakmontRoss Kinnaird/GettyFescue at Oakmont promises to terrorize golfers.

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