Rory McIlroy knows being disciplined will be vital as he prepares for a "great test of golf" in the U.S. Open at the daunting Oakmont Country Club this week.

The Pennsylvania course is regarded as one of the toughest in the world, with lightning quick greens, thick rough and an array of bunkers to contend with.

McIlroy is aware that he will have to adapt in order to tackle the challenge that lies ahead as the world number three targets a second U.S. Open title, which would take his tally of majors to five.

The 2011 U.S. Open champion said on Tuesday: "You have to be so disciplined here.

"One of the real challenges about this golf course, especially after they've taken so many trees away, is it's a big, wide open space now, and you're hitting into these tight fairways, and there's not really a whole lot of definition out there.

"So you have to be so zoned in to where you want your targets to be. It's probably a little easier for us this week than it is for the members, because we have grandstands to hit at and TV towers and whatever, whereas members play this course day in and day out, and they don't have anywhere to hit at out there.

"It's really hard to hit your targets off the tees and into the greens. We were talking on 16. For me, no matter where that pin is on that green, if you hit it at those two TV towers, try to land it seven or eight paces on the green, you're going to leave yourself a decent leave to whatever pin that is.

"So I think you just have to be really disciplined and trust the numbers, and you could go a whole round here without hitting it at any pin.

"And just trust that where you're hitting it into the spots is the best leave. I'd much rather have a 30-foot putt up the hill on these greens than even an eight-footer down the hill.

"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. It's a great test of golf. Every shot you hit, you're under pressure to hit a great shot because you can't really miss it.

"You have to get the ball in play. You really need to put the ball on the fairway, and that's a huge premium.

"And if you get your ball on the fairway, you've just got to make sure that you leave yourself below the hole on the greens. And even in some cases, that may mean missing the green.

"So two keys for everyone this week is get the ball on the fairway, and when you can do that, keep it below the hole with your approach shot."

The Northern Irishman will play his first two rounds with Masters champion Danny Willett and Rickie Fowler - teeing off at 8.24am local time on Thursday.