William McGirt opened up a two-shot lead heading into the final round of the Northern Trust Open in California.

The American fired a six-under-par 65 to go 12 under overall and lead by a couple from George McNeill and Charlie Beljan - though he was on target for an even bigger lead until he bogeyed the 15th.

A host of players, including Bubba Watson, Jordan Spieth and Dustin Johnson, were within four shots of the leader heading into Sunday.

"It's just 18 more holes, and whatever is going to happen is going to happen," McGirt told pgatour.com. "All I can do is go out and play the best I can."

Padraig Harrington missed Friday's cut by two shots and Darren Clark did not appear on Friday because of a chest injury, after an opening 78.

Victory would be a big deal for McGirt as it would not only be his first on the PGA Tour but would also send him to the Masters and earn him a two-year exemption.

He carded eight birdies and two bogeys on Saturday, making a big move down the opening third of the course.

He birdied all of the opening six holes except the fourth, where he dropped a shot.

McNeill's 66 was highlighted by an eagle at the first, while Beljan, who carded 68, had one of his own at the 11th.

Watson carded seven birdies in a blemish-free 64 to thrust himself into contention, sitting alongside halfway leader Sang-Moon Bae, whose one-over 72 dropped him to eight under.

Lee Westwood was the leading European at six under following a 68, three clear of fellow Englishman Justin Rose.