LAS VEGAS, October 21, 2013 (AFP) - Simpson, who earned his fourth career win on the USPGA Tour, finished the tournament at 24-under-par 260.
"This year I felt like I have gotten better," Simpson said. "I just haven't gotten a win and I was close at Hilton Head, but we've been working hard and it's just nice to finish the year off with a W and get back to Hawaii."
Japan's Ryo Ishikawa (65) and Jason Bohn (66) tied for second place at Summerlin course at 18-under, while Charley Hoffman (64) finished alone in fourth at minus-17.
Luke Guthrie (64), Troy Matteson (64), Charles Howell (65) and Chesson Hadley (70) tied for fifth place at 16-under 268.
Simpson began the day with a four-stroke lead and quickly added to that with back-to-back 15-foot birdies at No. 2 and No. 3 to move to 21-under.
He easily maintained the lead from there.
"I was playing, good solid golf," he said. "I didn't look at any leaderboards all day, but the course is drying out and I knew it was playing tough.
"That three-putt (No. 12) kind of set me back a little bit, but it was nice to birdie 13 and then I made a couple more birdies, which is a good feeling."
He drained a long birdie putt on No. 9 to finish with a 32 on the front. That gave him a six-shot lead over five players.
A three-putt bogey at the 12th cut Simpson's lead to three, but he bounced right back with three birdies over his next four holes to pull away for good.
He parred his final two holes, including a 25-foot putt at 18, to close out the victory.
Bohn capped a run of five birdies over an eight-hole stretch with consecutive birdies at the 11th and 12th to pull within four of the lead at 18-under.
Leading fourth-round scores on Sunday in the $6 million US PGA Shriners' Hospitals Open (USA unless noted, par-71)
260 - Webb Simpson 64-63-67-66
266 - Ryo Ishikawa (JPN) 67-66-68-65, Jason Bohn 67-64-69-66
267 - Charley Hoffman 66-70-67-64
268 - Luke Guthrie 69-64-71-64, Troy Matteson 67-69-68-64, Charles Howell 67-69-67-65, Chesson Hadley 65-66-67-70
269 - Freddie Jacobson (SWE) 67-67-71-64, Ryan Moore 69-63-69-68, Jeff Overton 63-68-68-70
270 - Carl Pettersson (SWE) 68-67-69-66, Jimmy Walker 71-68-64-67, Brendon Todd 67-68-67-68