UPDATE 1-Golf-Spieth seizes six-shot lead at Pebble Beach

(Adds details, quotes)

* World number six one-putts 13 of his 18 holes

* Leads Snedeker by six heading into final round

Feb 11 (Reuters) - Jordan Spieth putted superbly on Pebble Beach's bumpy, rain-softened greens to surge six strokes clear after the third round of the weather-hit AT&T Pebble Beach Pro-Am on Saturday.

Joint leader when the fog-delayed second round was completed earlier in the day, the world number six fired a sparkling seven-under-par 65 on the picturesque Pebble Beach Golf Links, one of three venues being used for this week's event.

Spieth, eyeing his ninth PGA Tour victory, needed no more than one putt on 13 of his 18 holes as he posted a 17-under total of 198 to tighten his grip on the tournament.

Brandt Snedeker, a two-time former champion at Pebble Beach who is also considered one of the best putters in the game, carded a 67 on the same layout to finish the day alone in second at 11-under.

Spieth has been frustrated by his putting in recent weeks but found his touch on Saturday.

"I hit my lines today," the 23-year-old told Golf Channel. "There were a couple of putts that went in that I thought maybe had a chance to miss but other than that I hit my lines and they rolled right there which is a huge confidence boost for me.

"It's been something I've been struggling with, my putter this year, compared to what I would call is standard for myself.

"I've been striking the ball really well but my third and ninth place finishes were off of very average putting on strokes gained."

Spieth finished third at the Sony Open in Hawaii and tied for ninth at the Phoenix Open in his previous two starts on the PGA Tour.

"I definitely made up for it today and I hope to continue to tomorrow," said the double major winner.

Long-hitting Dustin Johnson, who was grouped with Spieth for the first three rounds, returned a 66 to share third at 10-under with Kelly Kraft (66).

"I played really well," said U.S. Open champion Johnson, who won back-to-back titles at Pebble Beach in 2009 and 2010. "I've been playing pretty solid all three days and I finally got a few putts to go in today.

"It's not easy to get the ball close to the holes and when you do it's hard to make putts. But I drove it really well and hit a lot of nice solid iron shots, so just a pretty stress-free day."

Australian world number one Jason Day had been tied for the lead at the tournament's halfway point with Spieth and Derek Fathauer but dropped five shots in his first six holes at Pebble Beach on the way to a 73 to end the round at seven-under. (Reporting by Mark Lamport-Stokes in St. Augustine, Florida; Editing by Peter Rutherford)