Mickelson began the final round six shots off the pace, but proceeded to fire the best round of the day by three strokes and cruised into the winner's circle.
He picked up his fourth win at Pebble Beach Pro-Am, finishing at 17-under 269.
Third-round leader Charlie Wi stumbled early but rebounded late to post an even-par 72 to grab sole possession of second place at 15-under 271.
Tiger Woods began in third place but missed several short putts Sunday, struggling to a 3-over 75 and sliding into a tie for 15th place at 8-under 278.
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