World number two Mickelson is a three-time major winner

Victory would seal the third leg of a "Mickelslam" - holding all four majors at once - and take him halfway to a Grand Slam of majors in the same year.

Kiwi Michael Campbell will defend the title he won at Pinehurst, while Tiger Woods returns the fray for the first time since his father's death in May.

Mickelson tees off at 1255 (BST) while Woods takes to the course at 1825.

Interview: England's Luke Donald

World number two Mickelson, who will be 36 on Friday, won the USPGA at Baltusrol last August and followed it up with his second Masters title at Augusta in April.

But the left-hander, a US Open runner-up in 1999, 2002 and 2004, refused to get carried away with his major streak.

"I'm just trying to win one, I'm not trying to win three," said Mickelson, who has won three times in his last nine major starts and posted four other top-10 finishes.

Woods, 30, is chasing his 11th major, which would take him to second in the all-time list alongside Walter Hagen, though still seven behind Jack Nicklaus.

I've never seen a tournament where he has not been prepared to win, unfortunately Phil Mickelson on Tiger Woods

The American has not competed for nine weeks since the death of his father Earl but he remains confident that he has not lost any of his form.

"I'm here to compete and play and try to win this championship," said Woods.

"I've had plenty of time to get ready. I know that Dad would still want me to go out there, grind it and give it my best."

The par-70 West Course at Winged Foot, New York, is the longest test in US Open history at 7,264 yards, and will feature the event's traditional thick rough, tight fairways and fast greens.

But this year, in a new move to silence criticism that US Open course's are sometimes unfair, event organisers the United States Golf Association (USGA) have introduced "graduated rough".

Three tiers of rough have been prepared, the first being cut at a generous one-and-a-half inches to line the fairway.

Six feet outside that, the rough will be cut at three inches with the third cut set at five inches to punish the most wayward drives.

Previously, there was only one very punitive cut that treated the mildly inaccurate the same as the wildly inaccurate.

My plan is to be a multiple major winner Defending champion Michael Campbell

So far the reaction from the players seems to be that the course is tough but fair, and double US Open champion Ernie Els is a fan of the new rough.

"I think it's a wonderful test of golf," said Els. "They have got it set up very well. The rough is tiered and I think all the players agree with that.

"The way it is set up right now is as fair as I have seen in a long time. It's a great layout.

"They have made some holes a lot longer than in 1997 (when Davis Love won the USPGA by five shots) but still I think this week is set up for the best player."

But Mickelson made it clear that while the course may be fairer than previous USGA creations, it is still very difficult.

"This golf course is set up for pristine conditions: zero wind, 80 degrees and warm," said Mickelson. "And if they don't get it, this course will be unplayable."

One of those will be Brighton-based Campbell, 37, who is rated a 100-1 shot despite his triumph last year after coming through a Walton Heath qualifier with a birdie on the 36th and final hole.

"Let Tiger, Vijay (Singh) and Phil (Mickelson) have all the attention and I can just do what I did last year," said Campbell, who would become the first back-to-back winner since Curtis Strange in 1988-89.

Garcia is perhaps the best player in the world without a major title

"I feel very comfortable being a major winner and being defending champion is a label I'm very comfortable with. I'm a person who rides on a wave for a very long time.

"Once you get the bug, once you win your first major you want more. My plan is to be a multiple major winner."

World number three Vijay Singh, back on form after taking the Barclays Classic, has yet to win a US Open despite two USPGAs and a Masters title.

South Africans Retief Goosen and Els, world ranked fourth and seventh respectively, are both two-time US Open winners, while Jim Furyk is the other member of the world's top 10 with a US Open victory to his name.

Spain's Sergio Garcia and England's David Howell, eighth and ninth in the world, head the 39 European Tour members in action, which also include English debutants Kenneth Ferrie, Phillip Archer, Graeme Storm and Oliver Wilson.

Europe's last major winner was Scot Paul Lawrie, who clinched the 1999 Open Championship at Carnoustie. The last US Open winner was Tony Jacklin in 1970.