Phil Mickelson watches his tee shot on the 12th hole during a practice round of the U.S. Open Golf Championship Monday, June 14, 2021, at Torrey Pines Golf Course in San Diego. (AP Photo/Gregory Bull)

SAN DIEGO — Phil Mickelson accepted a special exemption from the USGA with reason to believe this might be his last shot to finally win a U.S. Open.

Now he gets five more years, courtesy of his stunning victory last month at the PGA Championship that made him the oldest winner in 161 years of the majors.

The clock is still ticking, though.

Mickelson turns 51 on the eve of the U.S. Open, and Lefty is leaving nothing to chance. He took a few days to celebrate his sixth major title, and then it was time to get to work.

“It’s a unique opportunity because I’ve never won a U.S. Open,” Mickelson said Monday. “It’s in my backyard. I have a chance to prepare properly, and I wanted to put in the right work. So I’ve kind of shut off all the noise. I’ve shut off my phone. I’ve shut off a lot of the other stuff to where I can focus in on his week and really give it my best chance to try to play my best.”

If his victory at Kiawah Island was a surprise, this would be sheer fantasy.

Mickelson holds the wrong kind of U.S. Open record with his six runner-up finishes, most recently in 2013 at Merion, and it stands out even more considering it is the only major keeping him from joining the most elite group in golf with a career Grand Slam.

He is a three-time winner of the PGA Tour event at Torrey Pines, though to call it a home-field advantage can be misleading. It has been 20 years since Mickelson last hoisted a trophy at Torrey Pines, right before Rees Jones — known as the “Open Doctor” — overhauled the South Course with hopes the municipal course could host a U.S. Open.

Since then, Mickelson has missed the cut as often as he finished in the top 10 — five each — and he has rarely contended.

How much of that was the redesign? How much was attitude? Hard to tell. Mickelson has never lacked for enthusiasm — how else to explain how he has gone a record 30 years between PGA Tour victories? — though even he has questioned his effort at Torrey.

He grew up in San Diego and still lives here, but Torrey wasn’t his primary course as a junior and he never comes to Torrey except for the week of the PGA Tour event in January. That changed last week. Mickelson typically likes to play the week before a major. This time, he took two weeks off for a crash course.

“I put a lot of time in on the greens, because even though they’re not at tournament speed, I needed to relearn and see the breaks and know what the ball does on these greens,” Mickelson said. “Because when you see the way the ball rolls, you know where you have to be for your approach, and you know what kind of shot if the best shot to hit into certain approaches.

“Granted, I’ve played out here a bunch since the redo, but I really haven’t spent a lot of time to learn the nuances,” he said. “And I did that early last week.”

He spent Monday playing 18 holes with the defending champion, Bryson DeChambeau, and teenager Akshay Bhatia. Mickelson placed cup-sized placards on four quadrants of the green and putted from different angles.

There also was time for a teaching moment. He set a few balls short of the 18th green to hit some full-swing flop shots that went as high as they went far, about 12 feet. This wasn’t a shot he planned to play, rather an illustration of how to hit the shot. DeChambeau crouched and held his phone a few week from the turf to capture video as his swing coach looked on.