The Portrush golfer, starting on the back nine on the Californian course, birdied the par-five 17th and hit more two birdies on the front nine.
He also bogeyed the par-three seventh and is tied for 30th place, five shots behind American leader Sam Saunders.
Padraig Harrington is tied for seventh place on four under alongside Phil Mickelson.
Shane Lowry will struggle to make the weekend cut, having shot three over through 16 holes on a fog-delayed first round.
Dustin Johnson's bid to overtake Jason Day as world number one continued with a first-round five-under-par 66.
Graeme McDowell carded a two-under par round of 69 at the opening round of the weather-interrupted Genesis Open.