Four strokes off the pace going into the final round, the American left-hander seized control with five birdies in the first eight holes on the way to a flawless seven-under-par 64 at a sun-splashed Riviera Country Club.
Watson, who has long relished playing at the revered venue despite never having posted a top-10 finish in seven previous starts, finished up in style as he rolled in a 14-foot birdie putt at the last to post a 15-under total of 269.
Long-hitting American Dustin Johnson, one of four players who held at least a share of the lead during the final round, closed with a five-birdie 66 to finish alone in second place.
(Reporting by Mark Lamport-Stokes; Editing by Gene Cherry)
