Here’s a wild thought: At 54 years old, Phil Mickelson is showing signs of being a serious contender to win the Masters, which begins next week at Augusta, Georgia.

A three-time winner of the Green Jacket, Mr. Mickelson hasn’t accomplished much of anything since being among the first to leave the PGA Tour and defect to LIV Golf, the rival tour backed by Saudi Arabia’s Public Investment Fund, which has poached many of golf’s top stars.

A third-place finish in Hong Kong early last month was the best of Mr. Mickelson’s four-year LIV career. Although he tied for 19th at Singapore two weeks later, he has scored under par in five of his last six competitive rounds. Add that to his experience and knowledge of Augusta National, and Mr. Mickelson is expected to be a viable contender when the world’s best golfers assemble for the first major of the season.

“It’s the start of the major championship series,” Mr. Mickelson said on Tuesday at Miami, where LIV Golf is staging its latest tournament. “It’s almost a religious experience every time you set foot on Augusta National.”

Mr. Mickelson will be making his 32nd appearance at the Masters, after winning in 2004, 2006, and 2010.  The left-handed legend stunned the golf world in 2021 by capturing the PGA Championship at age 50, becoming the oldest major championship winner.

Despite his struggles on the LIV Golf Tour, Mr. Mickelson earned a tie for second at the 2023 Masters behind winner Jon Rahm, who later defected to LIV Golf, as did the 2017 Masters champion, Sergio Garcia.  Each winner has a lifetime invitation back to the Masters.

“To be part of the past history with the three of us having won there knowing that every time we go back we’re part of the history and we get to partake in everything that transpires that week and the way they treat the past champions, which is better than any tournament in the world, it’s just a special feeling to be a part of that,” Mr. Mickelson said.

The major championships — the Masters, the PGA Championship, the U.S. Open, and the Open Championship — are the only tournaments where players from the PGA Tour and LIV Golf compete in the same event. It’s more difficult for LIV golfers to qualify for the majors because they don’t receive world golf rankings due to the league’s 54-hole format, as opposed to the 72 holes played at the PGA tournaments.

The reigning U.S. Open champion, Bryson DeChambeau, and a five-time major winner, Brooks Koepka, are also among the LIV golfers who will be at Augusta.

Mr. Mickelson, a six-time major winner with 57 career wins as a pro, has taken much of the heat from PGA Tour loyalists for starting the trail of defections to LIV Golf. His game deserted him amid all the controversy.  He had just one top ten finish in 2023 and again in 2024 on the LIV Tour, which is why his third-place showing in Hong Kong raised eyebrows.  He was 14-under during his three rounds in Hong Kong and is 18-under during his last six rounds of competition.

Experience has always been a key at Augusta, as it’s the only major played at the same course each year. Mr. Mickelson’s biggest lesson learned was how to deal with the par-5 15th, where a pond protects the front of the green.

“It was the 15th hole [where] I would press the issue and I’d make 6, 7, a number of times trying to make 4,” he said. “When I finally accepted a 5 on that hole and tried to win it elsewhere, that’s when I seemed to finally break through. That was the hole that I felt like being more patient and taking a different strategy and not pushing the issue allowed me to ultimately take advantage of the other holes to win.”

Scottie Scheffler, who won his second Green Jacket last year, is the early favorite, followed by Rory McIlroy, Collin Morikawa, Ludvig Aberg, Mr. Rahm, Mr. DeChambeau, Xander Schauffele, and Justin Thomas.

Long once one of the most powerful players in the game, Mr. Mickelson is now relying more on accuracy than power. “I’ve got to find another way to beat these guys because I’m not going to overpower them,” he said recently, adding he’ll use Miami “to get sharper and sharper and feeling that pressure and excitement that only gets me more ready for Augusta.”