Mickelson was one of a host of big name players to miss the cut at the US Open Saturday, as Oakmont proved to be as tough as the pre-tournament predictions.
Also missing the US Open cut were former champions Rory McIlroy, Justin Rose and Ernie Els, while fan's favourite Rickie Fowler also failed to make the grade.
Mickelson, who came into Oakmont looking to complete a career Grand Slam, finished at seven over, one shot too high.
Instead of whining, Mickelson was circumspect with his comments about the punishing Oakmont course.
“I felt like it was a very fair set-up. If you played well, there were pins you could get to. You could make some birdies, said the five-time major winner.
“I actually thought I played really well except I let four or five par putts kind of slide. You can’t do that here because you don’t have those birdie opportunities to offset those mistakes.
“My irons were just a fraction off. Instead of hitting it 15 feet, giving myself chances, I’m 30 feet, 40 feet and fighting just to make par,” he added.
McIlroy, meanwhile, has been struggling for form in recent months. He carded a one-over par 71, which added to his first round 77, left him two over the cut-off point.
Fowler missed the cut at the US Open for the second-straight year after finishing 11 over, but didn’t appear too disheartened.
"I felt like I drove it well in the practice rounds," Fowler said. "Yeah, just struggled to kind of get the confidence built up and just go out there and trust it. So made some good swings today, though, some not so good."
The Northern Irishman needs to win to reclaim the world number one spot from Jon Rahm.
The 56-year-old, who is already the oldest winner on Tour, shot a 64 to claim a share of second place.
Rory McIlroy is excited about the jam-packed schedule that lies ahead.
The American is now sixth in the world rankings.
The world number 89 blamed a new putter as he laboured to a closing round of 77 at the British Masters.
Rahm replaced Rory McIlroy at the top of the rankings following his victory in the Memorial Tournament.
Seven years of hard work paid off in spectacular fashion for Michael Thompson at the 3M Open on Sunday.
Thompson carded birdies at the 16th and the last to secure his second PGA Tour win of his career.
Tom Lewis, the only Briton to make the cut, will start the final round eight shots off the lead.
The 23-year-old won a second European Tour title.