Updated

Las Vegas, NV (SportsNetwork.com) - Webb Simpson fired an 8-under 63 on Friday to grab a 4-stroke lead at the end of two rounds of the Shriners Hospitals for Children Open.

Simpson, who is seeking his fourth career win on the PGA Tour and first since the 2012 U.S. Open, finished 36 holes at TPC Summerlin at 15-under-par 127. His 4-shot lead is the largest in tournament history.

"I haven't won this year, but my one goal every year is to get better, and I felt like I got better," said Simpson. "I was happy to finish the Tour Championship with a good, solid tournament. Getting better, so that's all I care about."

Jason Bohn flirted with 59 during his second round, but struggled down the stretch to card a 7-under 64 and move into a group of five players tied for second place at 11-under 131.

First-round leader J.J. Henry is among that group after following Thursday's course-record setting 60 with an even-par 71 on Friday. Also sharing second is John Senden (66), Chesson Hadley (66) and Jeff Overton (68).

Ryan Moore (63) and Brian Stuard (65) occupy seventh place at minus-10.

Simpson started on the back nine and opened his round with an 8-foot birdie putt at the 10th.

After parring his next two holes, he capped back-to-back gains at the 13th and 14th with a 20-foot putt to move to 10-under. He found water at the 16th en route to a bogey, but got that stroke back at the 18th with another lengthy birdie putt.

He made it two in a row with a 14-foot putt at the first, and later surrounded a 34-foot birdie putt at the fifth with a pair of birdies from inside 10 feet at Nos. 4 and 6 to move to 14-under.

He closed his round with a birdie at the ninth to head into the clubhouse with the lead.

"I hit a couple loose shots today, but really managed to make putts and take advantage of the holes you got to make birdie on," stated Simpson. "The course was set up good again, some tough pins and we stayed away from the trouble. Thankful to shoot another good one."

Bohn's round began with consecutive birdies from inside six feet at the first and second before he poured in 13-foot birdie putt at the fourth to reach 7- under.

He stayed hot with back-to-back gains at the sixth and seventh -- capped by a 16-foot effort -- and added another pair of birdies at the ninth and 10th to move to 11-under.

A 38-foot birdie putt at the 12th placed him at 8-under for the day and in position to shoot 59, as he needed to play his final six holes at 4-under to reach the number.

Bohn could not keep up his torrid pace, however, and after parring his next three holes, he followed a birdie at the 16th with a double-bogey 5 to fall back to minus-11.

His disastrous hole started when he found a greenside bunker with his tee shot. He then blasted past the green with his next before chunking his par attempt, leading to his eventual double bogey.

Bohn 2-putted for par at the last to maintain his share of second place.

Senden recorded five birdies during his bogey-free round, while Hadley traded three bogeys with eight birdies to match Senden's 66.

"It's been a fantastic start to the week, and to have a chance going into the weekend is awesome," Hadley said. "(I'm) just looking to manage the nerves tomorrow and just realize it's just golf, and let's just go have some fun."

Overton countered three bogeys with six birdies during his second round. Henry posted four bogeys and four birdies during his up-and-down round.

NOTES: Simpson's previous best finish at this event was a tie for fourth in 2010 ... Simpson has recorded six straight rounds at TPC Summerlin at 66 or better ... Simpson has failed to convert his three career second-round leads into a win ... Bohn has never shot an over-par round at the Shriners Hospitals for Children Open ... Patrick Reed withdrew during the second round with a wrist injury ... The cut line was set at 3-under-par 139, with 71 players advancing to the weekend. Among those to miss the cut was Andres Romero, who followed Thursday's 61 with a 10-over 81 during his second round.