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.

The endorsement came after Mr Rajoy's Popular Party (PP) gained the backing of the Ciudadanos ("Citizens") party and tacit support from the Socialists.
Socialist lawmakers are said to have been among the 68 abstentions.
The country had faced the prospect of a third general election inside a year.
But the Socialists forced out their leader, Pedro Sanchez, earlier this month after he rejected abstention.
Mr Rajoy has led a caretaker administration since losing his overall majority in an election last December. A repeat election in June failed to end the impasse but strengthened his hand.
The Socialists (commonly known by their Spanish abbreviation, the PSOE) came second on both occasions, their support eroded by radical leftist newcomers Podemos.
For decades, the PSOE and PP took turns in governing the country on their own but last year the popular vote split four ways - the new centrist Ciudadanos party came fourth.
Spain country profile
The PSOE has 85 seats to the 137 won by the PP in June.
Podemos's Ikea-style appeal to young voters
Resisting change in a dying Spanish village
Taking back Barcelona's apartments
Graeme McDowell carded a two-under par round of 69 at the opening round of the weather-interrupted Genesis Open.
[NEXT_CONCEPT]
Spain's parliament has voted to allow conservative leader Mariano Rajoy to lead a minority government after a 10-month political deadlock following inconclusive elections.