(Reuters) - Former U.S. Open champion Webb Simpson wielded a red-hot putter as he piled up nine birdies to charge into a four-shot lead in Friday's second round of the Shriners Hospitals for Children Open in Las Vegas.
American Simpson, who teed off at the par-four 10th hole, had only one bogey on his way to an eight-under-par 63 at the TPC Summerlin in the second event of the PGA Tour's 2013-14 season.
The North Carolina native, who won last year's U.S. Open at Olympic Club in San Francisco, birdied five of his last nine holes to post a 15-under total of 127.
Fellow Americans Jeff Overton (68), Jason Bohn (64), JJ Henry (71) and Chesson Hadley (66) plus Australian John Senden (66) share second place four off the lead at 11-under.
Bohn matched Simpson's nine birdies but carded a double bogey five on the penultimate hole to drop back.
"The ball was really going far," Simpson, 28, told Golf Channel after hitting 15 of 18 greens in regulation and needing only 24 putts.
"I was wondering why scores were so low yesterday but the course played a little shorter than I thought it would.
"I just putted well and kept it going. I think guys are going to keep making birdies so I've got to keep the hammer down."
The TPC Summerlin regularly yields low scores in the high Nevada desert where fine weather, thin air and smooth greens usually lead to birdies galore. American Ryan Moore won last year's title with a 24-under total and also shot a 63 on Friday to move into a tie for seventh at 10-under.
"I think the one synonymous thing is patience, because the U.S. Open you obviously have to remain patient because you're not going to make many birdies," Simpson said.
"But here it's not like every hole is a birdie hole so you have to remain patient because birdie runs come. You have to stay patient because you'll get on those runs too."
Simpson finished on a high note with a birdie on his final hole, the par-five ninth, despite a poor drive that forced him to lay up, before he struck a nice approach shot to nine feet.
Earlier, he rolled in a 25-footer at the par-four sixth, after hitting it to inside 10 feet at the previous hole.
While the world number 24 has not won since his U.S. Open breakthrough, he has been in consistent form. He has not missed a cut since early June and is coming off a fourth-place finish at the 2013 season-ending Tour Championship.
Simpson also played on the U.S. team that won the Presidents Cup earlier this month.
"I haven't won this year, but my one goal every year is to get better, and I felt like I got better," Simpson said.
"I was happy to finish the Tour Championship with a good, solid tournament. Getting better, so that's all I care about."
Among the surprises to miss the three-under cut were International team Presidents Cup members Graham DeLaet, Brendon de Jonge and Angel Cabrera while Cabrera's Argentine compatriot Andres Romero went from second place with his 10-under 61 to a 10-over 81 to freefall out of the tournament.
(Reporting by Andrew Both and Ben Everill; Editing by Mark Lamport-Stokes/Peter Ruiherford)