The American has been a runner-up at his national championship on six occasions, most recently in 2013 when he finished two shots behind Justin Rose, and he is yearning for the chance to complete a career grand slam of the four majors.

"I don't feel that sense of urgency ... it's something I really would love to do is complete the career grand slam," Mickelson said after playing a practice round with fellow Americans Brandt Snedeker, Rickie Fowler and Jimmy Walker.

"I'm in the best shape I've been in. I've always felt a long golf swing - a long, smooth, flowing swing - leads to a long career, and a short, violent swing leads to a short career.

"And I haven't had any really long-term or debilitating injuries to speak of. So if I continue to do what I've done the last eight months or so, there's no reason why I couldn't play at a high level for a while."

Mickelson could become the second-oldest US Open champion behind Hale Irwin, who was also 45 when he secured the 1990 title.

Left-hander Mickelson has displayed encouraging form in his last five PGA Tour starts, culminating in a tie for third at the FedEx St. Jude Classic on Sunday when he closed with a 65, and no other winner would be more popular at Chambers Bay.

In 2013, he clinched the one major he had always felt was the most difficult for him to win, the British Open, with a brilliant closing round of 66 at Muirfield and his already stellar career would be made complete with a U.S. Open title.

Mickelson loves the look of Chambers Bay, a links-style layout adjacent to Puget Sound which will host the first U.S. Open to be played in the Pacific Northwest.

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