Timeless awe Phil Mickelson is attempting to complete a career Grand Slam by winning the US Open upon becoming golf's oldest major champion by winning the PGA Championship.

On Sunday, the 50-year-old American left-hander won an iconic victory for the ages – and the aged – with a two-stroke victory at windswept Kiawah Island for his sixth major title.

“I've felt for some years now, despite my lack of success, where I could still play at my finest and compete in big tournaments,” Mickelson stated. “But I hadn't demonstrated it to myself or anybody else until this week.”

Mickelson, who has overhauled his mind and physique through hard work and discipline, has found the fresh motivation to challenge the US Open, the massive one he has never triumphed and a tournament in which he has a record six runner-up finishes, a most recent in 2013.

The US Open will be in next month at Torrey Pines, near Mickelson's home in San Diego, and he turns 51 on June 16, the eve of the first round.

“I feel that if I remain mentally alert I will be able to perform well at Torrey Pines,” Mickelson stated. “I know I'm playing well, and this may be my last decent chance to win a US Open, so I'm going to give it all.”

Mickelson has to win the US Open to join Tiger Woods, Jack Nicklaus, Gary Player, Gene Sarazen, and Ben Hogan as the only golfers in history to win all four major championships.

“I'll take two weeks break before and go down to Torrey and spend some time on the greens, attempting to be ready for that week,” Mickelson said.

“Lefty” still hadn't won a big trophy since the 2013 British Open, but he has worked hard to shake the previous age record of 48 established by American Julius Boros at the 1968 PGA Championship.

“Undoubtedly it requires more energy from me, but there's no reason why I can't give it everything out there for 18 holes if I practice a little tougher, invest some more hours in the gym, eat properly, and practice hard,” Mickelson said.

“There seems to be no reason why you can't achieve your goals as you become older. It will only demand extra work. Nothing is impossible to achieve if you put in the hard work.”

For Mickelson, staying calm under pressure has involved clarifying his thoughts through meditation.

“Just the opportunity to calm my thoughts and also get rid of all the outside noise,” he explained. “I don't want to go all spiritual, but it has been the most essential thing for me.

“I've attempted to block out a lot of what's going on. I wasn't watching television. I wasn't answering my phone. I was just trying to keep things peaceful.”

It also means Mickelson, who fasts 36 hours each week, is monitoring what he eats a lot more than he used to, in part to combat psoriatic arthritis.

“I need to consume a lot less, and I need to eat healthier. I just can't eat much, and I need to rest my body,” Mickelson explained.

“This has been a gift for me because I feel better, there is no inflammation, and I wake up feeling fantastic. It was a worthwhile sacrifice.”

Over the last nine months, Mickelson played 16 events without a top-20 result, but he played an all-time classic to beat Father Time.

“If I'm being serious, this may be the last event I ever win,” Mickelson remarked.

“But it's also conceivable that I've had a breakthrough in some of my concentration and that I've been on a decent run.”

The idea is that there was no explanation why I or anyone else cannot do it later in life. It just requires a little more effort.”

Mickelson said that it had been difficult not to see consistent results before this week.

“It's quite thrilling because I've made a couple of breakthroughs in terms of being able to be more aware, more focused, and physically I'm smashing it and playing as good as I've ever done,” he added.

“Even though I believed it, there was a lot of uncertainty until I finally accomplished it.”