Whether it was continuing to be a part of U.S. Ryder Cup and Presidents Cup teams, finding a new workout routine, changing coaches, discovering a healthier diet, befriending - and needling - tour players who are young enough to be his son, Mickelson did his best to stay young.
RIGHT: Mickelson leads by three shots with two holes to play on Monday.
Instead, he had to return early Monday morning to complete his 44th PGA Tour victory, claiming a fifth AT&T Pebble Beach National Pro-Am while also becoming the eighth-oldest victor in PGA Tour history. He also became the oldest-ever PGA victor at the famed California coastal layout.
"It's been a very special week for me and this is a very special place to me".
It's the course where his grandfather worked as a caddie and where he began his pro career.
What excites him is that he's putting as well as he has at any time in his career and has found an extra "5-6 miles per hour swing speed" he believes that could be the key at the Masters, even if he conceded that winning 50 times on the PGA Tour might prove a challenge.
Mickelson has come close, with six runner-up finishes at the U.S. Open.
And while he enjoyed the victory, Mickelson didn't consider it meaningful in any way for the US Open.
"It's nothing like the course we'll see", Mickelson said. Another feature of Pebble Beach is the scenic 17-Mile Drive that offers drivers and passengers views of the golf course, seascape and spectacular mansions.
American Scott Stallings is third at 14 under, while South Korea's Si Woo Kim and Scott Langley are a shot back.
Casey called Mickelson's effort "a phenomenal round of golf" but added: "It's not over yet".
After an early birdie, Casey struggled to make anything happen.
Resuming again after the delay has not affected momentum for the final group, with England veteran Casey and Mickelson tied at 16-under-par.
"I thank Paul for having us come back out here this morning", Mickelson said.
"Sometimes I get in my own bubble", Mickelson said.
"I really don't think there's any carryover from here to the U.S. Open", he said after the victory. And in 1992 he made his first start as a professional at the Pebble Beach Pro-Am.
Mickelson hit 7-iron to 8 feet on the par-3 17th and played it safe down the par-5 18th, making a 6-foot birdie for a three-shot victory. Casey at least birdied the 18th for a 71 to finish alone in second, the difference of $152,000. But he said he understood Casey's perspective. "I worked on some things, warm-up routines - I've worked hard on the putting, and it's starting to pay dividends".
This was a fantastic win for the 27-year-old, a protege of fellow Aberdonian and former Open champion Paul Lawrie. "We weren't going to get 18 done".