By Mark Lamport-Stokes

OAKMONT, Pennsylvania (Reuters) - Rory McIlroy has already won four major titles but says that a victory at this week's U.S. Open being played at treacherous Oakmont Country Club could rank as his greatest ever accomplishment.

All four of McIlroy's previous wins in golf's blue riband events have been achieved on soft layouts where the scoring has been low, very different from Oakmont where the last U.S. Open champion here, Angel Cabrera in 2007, finished at five-over par.

"I'd be very proud if I won on a golf course like this," the Northern Irish world number three told reporters on a sun-splashed Tuesday at Oakmont after playing a practice round on the par-70 course.

"The majors that I have won have been soft and under par and (they) more suit my style of game.

"To be able to win on a course like this with the conditions the way they are, it would probably be my biggest accomplishment in the game ... would make me feel like a more complete player."

McIlroy announced himself as a potential golfing great with a stunning eight-shot win to claim his first major title in the 2011 U.S. Open at Congressional, becoming the championship's youngest winner since 1923.

He has since clinched the PGA Championship (in 2012 and 2014) and the British Open (in 2014) with a spectacular game marked by his high ball flight and an often aggressive approach.

"With experience, you learn what a good score is on that particular day or if you're not playing so well, how to grind it out and make pars ... get it in the clubhouse at a respectable score," McIlroy said of the strategy required at U.S. Opens.

"And I feel like just over the years I've learned how to do that a little bit better. That just comes with playing tournaments and being experienced and knowing what the conditions are like.

"But I definitely feel like I'm a more disciplined and more experienced player than I was a couple of years ago. I can see nothing but a benefit of that this week."

McIlroy was in a confident mood ahead of Thursday's opening round, having won his 13th European Tour title at last month's Irish Open before tying for fourth at the PGA Tour's Memorial Tournament in his most recent start.

"I'm obviously excited to be here," said the 27-year-old from Holywood in County Down. "I feel like my preparation leading up to this tournament has been pretty good.

"The last couple of competitive starts, I feel like I've played pretty well. I feel as prepared as I can be coming in here, and I feel like I've got a good game plan for the course. It's just a matter of going out there and executing it."

(Editing by Frank Pingue)