He was posing with the trophy.
For the first time in 102 tournaments around the world, dating to the summer of 2013 when he won the British Open at Muirfield, the 47-year-old Mickelson showed he still had the stuff to beat players who weren't even born when he collected the first of his 43 victories on the PGA Tour.
"This is a very meaningful win," Mickelson said after beating Justin Thomas in a playoff. "I can't really put it into words given the tough times over the last four years, and the struggle to get here, and knowing that I was able to compete at this level but not doing it.
"To finally break through and to have this validation means a lot to me."
Mickelson, who closed with a 5-under 66, was at his best over the back nine, with as many as six players still in the mix.
Suddenly two shots behind when Thomas (right) holed out from 119 yards for eagle on the 18th hole, Mickelson played a high-risk shot through the smallest of gaps in the trees to escape with par on the 14th. That's when he saw the score, and he followed with a two-putt birdie on the par-5 15th and a 20-foot birdie on the 16th.
Thomas, who won last week in a playoff at the Honda Classic, capped off a 62-64 weekend with more clutch play, no shot bigger than a sand wedge that bounced behind the flag and spun back into the cup on his final hole for eagle .
The playoff—the sixth in the last eight weeks on the PGA Tour--lasted only one hole. On the par-3 17th, Mickelson parred, and Thomas bogeyed for the second time on Sunday.
Thomas’ gap wedge shot on the playoff hole sailed too far, and his chip was too weak. Mickelson's 18-foot birdie putt rimmed around the edge of the cup, and Thomas missed his par from just inside 10 feet.
The disappointment was tempered only by his start — Thomas was 11 shots back going into the weekend — and by the guy who beat him.
"Man, there's nothing for me to hang my head about," Thomas said. "To even have a chance to win this golf tournament after where I was through 18, through 36 holes, I'm very proud of myself. Obviously, I would have loved to drum him out there in that playoff, but I'm just happy for him. ... He's playing some great golf."
Mickelson, his confidence higher than the 7,800-foot altitude in Mexico City, believes this is just the start.
"I don't think that this is the peak," he said. "I think I'm going to continue to get better."
This was far more than a duel between Mickelson and Thomas, who is 23 years younger. Tyrrell Hatton was right there, stride for stride, putting four straight 3s on his card with a stretch he capped off with an eagle on the 15th to tie for the lead.
But on the final hole, Hatton missed the green to the right, chipped 10 feet by and missed the par putt for a 67 to fall out of a playoff.
"I can't believe that I'm not at least in the playoff," Hatton said, still seething over a par putt on the 18th that started bouncing right after he hit it.
Mickelson won his third World Golf Championships title and, just a month after being on the verge of falling out of the top 50 in the world for the first time in two decades, moves to No. 18 in the world.
Shubhankar Sharma, the 21-year-old from India who started with a two-shot lead, didn't make his first birdie until the 12th hole. He finished with consecutive bogeys for a 74, six shots behind in a three-way tie for ninth. That will leave him on the bubble at No. 66 in the world for making it back to the next World Golf Championship, the Dell Match Play, in three weeks in Texas. Sharma first flies home for the Hero Indian Open next week.
"A little bit disappointed," Sharma said. "I was leading, and I couldn't finish it off today. But that's what the game is about. And what I learned today, especially playing with Phil, I'll cherish it forever."
Hatton tied for third with Rafa Cabrera Bello, who holed a bunker shot for eagle on the opening hole and was among six players who had at least a share of the lead during the final round.
Mickelson was the first player who appeared to seize control with a birdie on No. 10 to take the lead, and he was poised to pull away with a reachable par 5 at No. 11 and a drivable par 4 at No. 12.
Instead, Lefty made it as entertaining as ever.
Going for the green from light rough with the ball below his feet on his second shot at the 11th, Mickelson hooked it deep into the bushes to the right of the green, and played his next one from there, though he could barely see the golf ball. His shot hit the gallery and stayed in the trees, and his fourth shot narrowly missed another tree before settling 10 feet away. He made bogey, and just like that, it was a sprint to the finish 7,800 feet above sea level.
Mickelson made good on his assertion earlier this year that more victories were in store for him. He has four consecutive top 10s for the first time since 2005.
That also was the last time he had won in a playoff.
It all seems so long ago — playoffs, trophies, consistent play. Now he's just more than a month away from The Masters, and feeling invigorated.
And feeling like a winner.