Padraig Harrington, boosted by a red-hot putter, charged into a three-shot lead with a sparkling eight-under-par 63 in the Nissan Open first round.

The Irish world number 10, playing his first tournament at Riviera Country Club, reeled off 10 birdies and two bogeys to card his lowest score on the PGA Tour.

"I'm exceptionally pleased shooting 63," Harrington told reporters after making the most of near-perfect conditions in the morning.

"I played nicely, holed the putts and got the breaks, pretty much everything you need to do to shoot 63, really.

"Whenever I did miss a shot today, it seemed to be okay," added the Dubliner, who needed only 26 putts in his round.

"It's a tight golf course with a lot of difficult pin positions and I will make mistakes between now and the end of the week."

Masters champion Phil Mickelson, hot favourite this week after cruising to a five-shot victory at the Pebble Beach National Pro-Am on Sunday, shot a bogey-free 66 to lie joint second with fellow Americans Briny Baird and Pat Perez.

Although delighted with his own performance, Mickelson applauded Harrington's 10-birdie display on one of the most challenging of the classic US courses.

"It is a little humbling to shoot what I thought was a good round and then get lapped by three," Mickelson said. "That was an incredible round that he played. The greens were firm and a lot of the pins were tough to get at."

World number two Jim Furyk returned a five-birdie 67, a score that was matched by Spaniard Sergio Garcia, Britain's David Howell and Americans Cameron Beckman and Kevin Stadler.

Of the other big names, three-times major winner Vijay Singh and US Open champion Geoff Ogilvy opened with 68s while Ernie Els, who won at Riviera in 1999, carded a 69.

Six players were still out on the course when play was suspended for the day in fading light, Ireland's Paul McGinley the best of them at two under with two holes to play.