Mickelson had to return to Pebble Beach on Monday to complete his 44th Tour victory and did so easily, finishing at 19-under par with a 65.
Hail covers the second green of the Pebble Beach Golf Links during the final round of the AT&T Pebble Beach Pro-Am golf tournament on Sunday, February 10, 2019, in Pebble Beach, California.
Casey simply couldn't see, and we realized it was not possible to finish all 18 holes - "We can't finish two holes in six minutes", he said to the official - he opted to mark his ball on the 16th green.
"It means a lot to me to play the final round as focused and as well as I did", said Mickelson, who started the final round three strokes behind Casey. He won that summer's British Open at Muirfield and last year's Mexico Championship.
Third-round leader Paul Casey, who mixed two bogeys with two birdies, was at 15 under with three holes remaining, tied with Scott Stallings who finished with a 66. Six runner-up finishes, some in the most heartbreaking fashion, dot his career, the tournament keeping him from a career Grand Slam.
His brilliant play still shared the stage with weather that was freakish even by Pebble standards.More news: Julian Edelman shaves beard during taping of 'The Ellen Show'
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Greens quickly were covered by the tiny white pellets, and workers went from using squeegees for excess water to power blowers to remove the hail. Patrick Reed's brother laid on his back and tried to make a snow angel.
Mickelson began by calmly knocking his tee shot on the par-three 17th to inside 10 feet and Casey followed suit, but when the 41-year-old failed to sink an eight-footer for birdie his hopes of snatching the win were effectively ended. "I totally get where he's coming from", he told reporters Sunday.
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.
Some players finished in the dark with no chance of winning, but showed the effect of playing without light.
Jason Day and Kim Si-woo are tied for fourth place at 13 under.