By Mark Lamport-Stokes PACIFIC PALISADES, California (Reuters) - Former champion Bubba Watson charged into an early share of the lead at one of his favorite venues while Rory McIlroy also flourished on his tournament debut at the Northern Trust Open on Thursday. Left-hander Watson took advantage of a Riviera Country Club layout softened by overnight rain as he fired a five-under-par 66 in dazzling sunshine to join fellow Americans Chez Reavie and Luke List atop the first-round leaderboard. Northern Irishman McIlroy, making his first PGA Tour start of the year, was one stroke back after mixing five birdies with a bogey to finish level with Americans Ricky Barnes, Charles Howell III and amateur Charlie Danielson. More...