He was trying to sharpen his game, figure out what it will take to win a U.S. Open, and to make enough putts with his claw grip to avoid losing a practice match to two players whose combined age is younger than him.
This major has a reputation as the toughest test in golf.
It's every bit of that for Mickelson.
"I really believe that this week is testing a player's entire game," Mickelson said. "Because it forces you to make good decisions, to choose the right club off the tee, hit solid iron shots into the green and utilize your short game to save strokes. It's just a wonderful test ... the best test I've seen to identify the best player."
His definition of Pinehurst and its rugged, natural look would seem to require every ounce of concentration.
And that could be his biggest challenge.
On the golf course, Mickelson is trying to ignore the enormous expectations on him this week. He holds the worst kind of U.S. Open record with six runner-up finishes. He needs this major to complete the career Grand Slam.
And he's a sentimental favorite at Pinehurst No. 2, where in 1999 he played the entire week knowing his wife was on the verge of delivering their first child. Payne Stewart made a 15-foot par putt on the final hole to beat him by one shot. Amanda Mickelson was born the next day. Stewart died in a plane crash four months later.
"Payne and I had this moment where we talked about fatherhood, but he also talked about winning future U.S. Opens," Mickelson said. "Although I haven't won one yet, I'm still fighting hard, and this would be a great place to break through and do it. The flip side is that I tend to do well when it's least expected.
"I don't want to put the pressure on that this is the only week that I'll have a chance. I think I'll have a number of great opportunities in the future years. But this is certainly as good a chance as I'll have."
Off the course, Mickelson has made headlines that threaten his clean image. He was linked two weeks ago to an insider trading investigation involving activist investor Carl Icahn and Las Vegas gambler over some trades of Clorox stock three years ago.
FBI agents even came to the golf course to try to interview Mickelson. He referred them to his attorney, said he had done "absolutely nothing wrong" and "I'm not going to walk around any other way."
It would seem to be a major distraction for Mickelson.
Even though he hasn't won in nearly a year, and he has dropped to No. 11 in the world ranking, he is the center of attention in the sand hills of North Carolina - especially with Tiger Woods still out of the game while recovering from back surgery.
Then again, it could be to Mickelson's advantage to be at a place such as Pinehurst. The course doesn't allow anyone to think about anything but the next shot.
As for that other match? Mickelson carried the load as he and Rickie Fowler rallied from 3 down to tie the match, only for 20-year-old Jordan Spieth to make a 20-foot birdie on the 17th, and 21-year-old Justin Thomas to drill a tee shot on the 18th hole to set up a par for the win.
Another close call. Mickelson should be used to that by now.