Watson, leading Phil Mickelson by a single stroke, drained a 15-foot putt for birdie on the 18th, forcing Mickelson to try for an eagle on the final hole to stay in it.
But Mickelson wasn't able to hole a wedge shot from the fairway, handing Watson the one-stroke win with a 16-under 272.
Watson, who made six birdies on the day, dedicated the win to his father, who died of lung cancer a few months after the golfer had taken his first career win last year in Hartford, Conn.
Jhonattan Vegas and D.A. Points both made charges, but finished a bit short. Vegas (68) ended tied with Dustin Johnson (66) for third place at 13-under 275 and Points (67) claimed sole possession of fifth one shot further back.
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