Golf-Johnson, Mickelson near the early lead at Riviera

Feb 16 (Reuters) - Big-hitting Dustin Johnson made a strong start in his bid to claim the world number one ranking this week by firing a five-under 66 that left him two shots off the early first-round lead at the Genesis Open at Riviera.

The reigning U.S. Open champion, who can claim the top ranking with a victory should incumbent Jason Day tie for third or worse here, made six birdies and one bogey to stand two shots behind Sam Saunders on the classic Los Angeles layout.

"Obviously, it would be great to get there but I'm focused on this week and this golf tournament, each shot that I'm hitting," said Johnson. "I just want to put myself in position to win on Sunday."

Saunders, grandson of the late Arnold Palmer, made seven birdies in a bogey-free round of 64 as he chases his first PGA Tour win in his 79th start.

Among the pack of seven golfers lurking three shots off the pace was Ireland's Padraig Harrington and American favorite Phil Mickelson, who displayed some of his short game magic to the delight of fans.

Mickelson surged up the leaderboard with an eagle at the par-five 17th where he banged his 317-yard approach off the greenside grandstand into deep rough.

But the big lefty turned trouble into triumph when he hoisted up a high, soft pitch that found the bottom of the cup.

Joining Johnson at five under par was J.T. Poston, a Monday qualifier for the event who holed out from the fairway to eagle the par-five first hole for a rousing start on a day when fog delayed play for about an hour.

Heavy rain was in the forecast for Friday, but the easy-going Johnson was unfazed.

"I like it either way, when it's soft or firm," Johnson told Golf Channel. "It's one of my favorite courses we play all year." (Reporting by Larry Fine in New York; Editing by Frank Pingue)