By Mark Lamport-Stokes

(Reuters) - Compelling storylines abound ahead of next week's U.S. Open in Oakmont, Pennsylvania where defending champion Jordan Spieth, Jason Day and Rory McIlroy will bid to add another major title to their impressive career resumes.

American young gun Spieth, a double major winner at age 22, will look to rebound from his stunning back-nine collapse at this year's Masters when he led by five strokes with nine holes to play and the coveted Green Jacket seemingly secure.

Australian world number one Day, the game's best player over the past 10 months, will seek a second triumph in the blue riband events after making his breakthrough at the highest level in record style at last year's PGA Championship.

Northern Ireland's McIlroy, who announced himself as a potential golfing great with a stunning eight-shot win to claim his first grand slam crown in the 2011 U.S. Open at Congressional, has his sights set on a fifth major title.

Of all the storylines swirling ahead of the year's second major championship, however, none is more compelling than the venue itself which is widely regarded as the toughest in golf and certain to provide a grueling challenge for the players.

The daunting par-70 layout at Oakmont Country Club, designed by Henry Fownes and opened for play in 1903, is a hilly course with very few flat lies and renowned for its slick, undulating greens which have been described by the players as "scary fast".

Oakmont, which will be hosting the U.S. Open for a record ninth time next week, was rated by Spieth as "the hardest test in all of golf" after he played there for the first time in practice last month.

"This is arguably the hardest course in America. It's normally the hardest U.S. Open, at least what history shows," Spieth told reporters.

"It's going to be a challenge. Especially if you fall behind early, you're going to want to try and make up shots here, and in any U.S. Open, you can't try and make up shots. You've just got to let the golf course come to you.

"I know that if you win a U.S. Open at Oakmont, you can go ahead and say that you've conquered the hardest test in all of golf."


Phil Mickelson, a veteran of 25 U.S. Open starts during his Hall of Fame career and a runner-up in his national championship a record six times without ever winning the title, agreed with Spieth about the difficulty of Oakmont.

"I really think it is the hardest golf course we've ever played," the American left-hander told reporters after visiting Oakmont earlier this week. "But it's a very fair test, even though it's hard.

"A lot of golf courses when they challenge you tee to green the way Oakmont does, they usually have a little bit of a reprieve on the greens, and you really don't at Oakmont. They're some of the most undulating, fast, difficult greens to putt."

Argentina's Angel Cabrera delivered a superb display of ball-striking to win the U.S. Open when it was last played at Oakmont in 2007, and yet he could manage only a five-over-par total of 285.

"They pride themselves on being the hardest golf course in the United States," McIlroy said of Oakmont and its members. "You hit it in the bunkers and you've got to go sideways; you hit it in the rough and you can't get to the green.

"Even if you hit it on the fairway, it's hard to hit the greens. So obviously par is going to be very much a premium there."

U.S. Opens are known for being the most exacting of the four major championships and at Oakmont it will be more important than ever for players to be able to grind out pars and to stay as patient as possible when the going gets tough.

"It's just one of those courses that you don't know when the ball's going to stop rolling a lot of times ... especially on the greens," said respected golf analyst and former United States Ryder Cup captain Paul Azinger.

"A lot of the putts you have to make are going to be the par putts - it's not how many birdies you make or how many bogeys you avoid. It'd be a great week to be unflappable."

While the 'Big Three' of Day, Spieth and McIlroy will command much of the pre-tournament focus at Oakmont, other likely contenders include long-hitting American Dustin Johnson, Sweden's Henrik Stenson and 2013 champion Justin Rose of England.

Also among the favorites are Americans Bubba Watson and Rickie Fowler, South Africa's Branden Grace and Louis Oosthuizen, Masters champion Danny Willett of England and rising Japanese talent Hideki Matsuyama.

(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Larry Fine)