The 43-year-old American was left distraught at Merion Golf Club outside of Philadelphia on June 16 when he finished runner-up for a record sixth time at the US Open, losing out this time to Justin Rose.
It was a huge blow to a player who is entering the twilight of his career and one many thought would be too tough for him to overcome.
Certainly not at the British Open where Mickelson has struggled over the years with the intricacies and special demands of links golf.
A third place finish at Troon in 2003 and a tie for second at Royal Lytham two years ago was all he had to show for 19 previous campaigns and there was little to suggest it would be any different this time.
But instead of licking his wounds at home, Mickelson got on the plane, family in tow, and flew to Scotland to play in last week's Scottish Open at Castle Stuart near Inverness.
He won that, his first ever senior level tournament win in Europe, and carried the momentum with him down to Muirfield to the east of Edinburgh where on Sunday he had what he called the most fufilling moment of his entire career.
"It's a huge difference in emotions, as you can imagine," Mickelson said, his right hand grasping tightly the Claret Jug that goes to the winner of golf's oldest tournament.
"And being so down after the US Open, to come back and use it as motivation, to use it as a springboard, knowing that I'm playing well and to push me a little bit extra to work harder, to come out on top, in a matter of a month to turn it around it really feels amazing.
"I thought that it could go either way. You have to be resilient in this game because losing is such a big part of it. And after losing the US Open, it could have easily gone south, where I was so deflated I had a hard time coming back.
"But I looked at it and thought I was playing really good golf. I had been playing some of the best in my career. And I didn't want it to stop me from potential victories this year, and some potential great play.
"And I'm glad I didn't, because I worked a little bit harder. And in a matter of a month I'm able to change entirely the way I feel."
He agreed though that learning to play on the links, of which there are very few in the United States, had been a long, and at times painful, process.
Mickelson's first taste of the links came when he played at Portmarnock, outside Dublin in the Walker Cup amateur team competition in 1991.
He enjoyed that experience and thirsted for more, but his focus at that time was on learning how to compete effectively on the non-links US PGA Tour.
"The conditions and the penalty for missed shots in The Open Championship are much more severe than we played then. And it took me a while to figure it out, I would say," he said.
"It's been the last eight or nine years I've started playing it more effectively, but even then it's so different than what I grew up playing. I always wondered if I would develop the skills needed to win this championship."
Next up for Mickelson is probably the greatest challenge of his sporting life – to complete the career Grand Slam by finally winning the US Open after so many near misses. He has already won the Masters three times and the PGA Championship and British Open once.
That would truly seal his legacy as one of the golfing greats, he believes.
"I think that if I'm able to win the US Open and complete the career Grand Slam, I think that that's the sign of the complete great player," he said.
"And I'm a leg away. And it's been a tough leg for me. But I think that's the sign. I think there's five players that have done that.
"And those five players are the greats of the game. You look at them with a different light. And if I were able to ever win a US Open, and I'm very hopeful that I will, but it has been elusive for me. And yet this championship has been much harder for me to get."
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