Two weeks later he boarded a plane back to California carrying the Claret Jug and Scottish Open trophy, not to mention a box or two of Fruit Pastilles for his caddie Jim Mackay.
It was a remarkable fortnight of golf from the left-hander, who had managed just two top-10 finishes in the Open in 19 previous appearances and had missed the cut at Lytham the year before.
More recently, he had also finished runner-up in the US Open for a record sixth time just five weeks earlier, taking a one-shot lead into the final round at Merion on his 43rd birthday, only to stumble to a closing 74 to finish two shots behind Justin Rose.
He spoke then of the “heartbreak” he would always associate with the US Open unless he could win one eventually, but bounced back to win the Scottish Open in a play-off with Branden Grace at Castle Stuart the week before his Open triumph.
“It’s a huge difference in emotions, as you can imagine,” said Mickelson, whose brilliant win at Muirfield leaves him needing a US Open victory to become just the sixth player to win a career grand slam in the Masters era.
“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 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 was able to change entirely the way I feel.”
Mickelson’s win made it three in succession for players over 40 after Darren Clarke in 2011 and Ernie Els in 2012, but that came as no surprise to Mackay.
“He looks forward. He works hard,” Mackay said. “How many people are going to build a practice facility in his yard post-40? He wants it.
“He’s stronger than he’s ever been, he’s fitter than he’s ever been, and he’s hungrier than he’s ever been. And you can’t underestimate how much he wants to compete and do well. When he’s 60-something years old he’s going to be on the putting green at Augusta thinking he has a chance. That’s just how he is built.”
The chances of Mickelson repeating his heroics 12 months on would appear slim, the 44-year-old’s only top-10 finish of the season coming in the Abu Dhabi Championship in January.
However, the five-time major winner has a 10-year streak of winning at least once every season to protect and after coming from five shots off the lead going into the final round at Muirfield, his boundless optimism is understandable.
“I’ll start getting ready for Hoylake and I’m optimistic about the end of the year,” Mickelson said after his first attempt to complete the career grand slam saw him finish 28th at Pinehurst last month.
“But I’m excited about the coming years, too. I think that this year has been a great learning year for me as far as certain areas of my game, but I haven’t quite peaked with them yet. But I feel like I actually learned a few things and picked up some things for the coming years.”