After slipping out of the world’s top 100, Mickelson had been handed a special exemption for the US Open at Torrey Pines before securing a new five-year run in the USGA event through his stunning success on Sunday at Kiawah Island, where he became golf’s oldest major winner less than a month before turning 51.
It seemed as though Mickelson’s chance of becoming just the sixth player after Gene Sarazen, Ben Hogan, Gary Player, Jack Nicklaus and Tiger Woods to win all four of the game’s majors had disappeared, but maybe not.
“If I’m being realistic, it's very possible that this is the last tournament I ever win,” admitted Mickelson as he savoured his sixth major victory and first since winning the 2013 Open Championship at Muirfield. “But it's also very possible that I may have had a little bit of a breakthrough in some of my focus and maybe I go on a little bit of a run, I don't know.
“'I’ve believed for some time now without success that I could play at my best and compete in major championships still, but, until this week, I haven't proven it to myself or anyone else. But I do believe that I believe that if I stay sharp mentally I can play well at Torrey Pines.
“I'll take two weeks off before that and go out to Torrey and spend time on the greens and really try to be sharp for that week because I know that I'm playing well and this could very well be my last really good opportunity, although I get five more, to win a US Open. So I'm going to put everything I have into it.”
Mickelson has finished runner-up in the US Open on no less than six occasions, most recently in 2013, but he missed the cut in last year’s event at Winged Foot.
He also suffered one of the most embarrassing moments of his career in the tournament at Shinnecock Hills in 2018, when he intentionally intercepted a putt and was hit with a two-shot penalty.
Mickelson was the sixth player aged 50 or over to take a lead into the final round of a major, the most recent before him having been Tom Watson when, at the age of 59 and chasing a sixth success in the event, he lost in a play-off against Stewart Cink after finishing with a bogey in the 2009 Open at Turnberry.
“I thought the 2009 Open Championship performance by Tom Watson was one of the greatest sporting performances, and he hit a perfect second shot (into the green at the 72nd hole), too,” said Mickelson. “He couldn't land it any better and it still went over. It was one of the greatest performances in the sport.
“And it's inspiring, yeah, to see people like that do it. There's no reason why you can't accomplish your goals at an older age. It just takes a little more work.
“There's no reason why the game of golf can't be the game for a lifetime. If you take care of your body and do it the right way, and now with the exercise physiology and technology that's out there, you can work out the right way to get your body to function right and play golf for a lifetime, so I'm appreciative of that.”
Julius Boros held the record as the game’s oldest major winner, having been 48 when he landed the US PGA Championship in 1968, with Jack Nicklaus having been 46 when he recorded his sixth Masters success in 1986.
Mickelson, of course, had come close to landing a second Claret Jug victory in 2016 at Royal Troon, where he was pipped by Henrik Stenson in an epic duel over the final two rounds, but wasn’t going to be denied on this occasion.
“Certainly one of the moments I'll cherish my entire life,” he said of a success that lifted him 83 spots to 32nd in the world rankings, reclaiming his place as the highest-placed left-hander from 45rh-ranked Bob MacIntyre.
“I don't know how to describe the feeling of excitement and fulfillment and accomplishment to do something of this magnitude when very few people thought that I could. But the people that believed in me, my wife, Amy, my brother and caddie Tim, my Andrew Getson and my manager Steve Loy, those are the people that continued to inspire me to get the best out of me.”
Meditation also helped Mickelson turn back the clock as he claimed a second Wanamaker Trophy triumph with a two-shot victory over double winner Brooks Koepka and 2010 Open champion Louis Oosthuizen after surviving a wee wobble on the back nine after finding himself five ahead with six holes to play.
“I worked harder, that’s the deal,” said Mickelson of a victory that moved him alongside Lee Trevino and Nick Faldo on six majors. “I just had to work harder physically to be able to practice as long as I wanted to and I've had to work a lot harder to be able to maintain focus throughout a round. That's been the biggest challenge of late.
“My desire to play is the same. I've never been driven by exterior things. I've always been intrinsically motivated because I love to compete, I love playing the game. I love having opportunities to play against the best at the highest level.
"That's what drives me and the belief that I could still do it inspired me to work harder. I just didn't see why it couldn't be done. It just took a little bit more effort.”