* Riviera fan Watson closes with a 68 * Scott and Kokrak tie for second * McIroy fades with a final-round 75 (Adds detail, quotes) By Mark Lamport-Stokes PACIFIC PALISADES, California, Feb 21 (Reuters) - Bubba Watson clinched the Northern Trust Open on Sunday for a second time in three years, sealing victory by one shot after a wildly fluctuating final round at sunny Riviera. A stroke in front overnight, the American left-hander twice fell two off the pace as first Adam Scott and then Jason Kokrak broke clear but he regained control of the tournament with two birdies in the last three holes. Watson, who has always loved playing on the iconic Riviera Country Club layout, shot 68 on a breezy afternoon to land his ninth PGA Tour title with a 15-under total of 269. More...