PEBBLE BEACH, Calif. -- An unlikely birdie on the 15th hole by Arron Oberholser allowed him to coast the final three holes Sunday and win the AT&T Pebble Beach National Pro-Am.

Oberholser enjoyed a proud, peaceful walk up the 18th fairway on his way to an even-par 72 and a five-shot victory, matching the largest margin in the 77-year history of the tournament. Sweeter still was capturing his first PGA TOUR event on a course he has played since he was a teenager, and a tournament he rarely missed.

But it required plenty of help -- first from Mike Weir, then from a tree.

Weir, tied with Oberholser going into the final round, went out of bounds on the second hole and was five shots behind after three holes. The former Masters champion staggered to a 78 and tied for third.

Oberholser's fiercest competition came from within.

"Most guys says the first one is the toughest to win because you've never done it before," Oberholser said.

Arron Oberholser adds a TOUR title to his two Nationwide Tour wins. (Condon/ PGA TOUR/ WireImage)

Oberholser had a six-shot lead with six holes to play when he took bogey from the fairway bunker on the 13th. A flared second shot on the par-5 14th went under a tree in the right rough, forcing him to punch out sideways and escape with a bogey.

Then came his tee shot on the 15th, even farther to the right. It hit the cart path twice and was headed for trouble when it bounced off a tree and kicked back into an opening. With a view of the green, Oberholser hit wedge into 8 feet and turned the mishap into a birdie to restore his margin.

"That was a good break," Oberholser said. "Those are the breaks you need to win."

Oberholser finished at 17-under 271, five shots ahead of Rory Sabbatini. Weir finished six shots back.

"My wedge game and putting was what killed me," said Weir. "When you hit 13 of 14 fairways and shoot 78, your wedge and putting is not very good."

Sabbatini closed with a 70 to finish second, although he was never a factor.

Oberholser won in his 76th start on the PGA TOUR, and became the first player since Matt Gogel in 2002 to make the AT&T Pebble Beach National Pro-Am his first TOUR win.

He earned $972,000, but lost a week off.

Oberholser had planned to move into a new house in two weeks, but his victory likely will move him into the 40 in the world ranking, easily qualifying for the World Golf Championships-Accenture Match Play Championship at La Costa.

The 31-year-old Oberholser grew up in San Mateo and played college golf at San Jose State. There were cheers of "Go Spartans" throughout a final round of warmth and sunshine on the Monterey Peninsula.

He wanted to purge memories of two years ago at Pebble Beach when he was tied for the lead going into the final round, only to watch Vijay Singh put him away early with three straight birdies.

Sunday also turned suddenly, but not how anyone imagined.

From the middle of the fairway on the par-5 second hole, Weir hooked his approach shot off the road and out of bounds to take double bogey, and Oberholser got up-and-down from a bunker for birdie and a three-shot lead. On the next hole, Weir went over the green and made bogey, while Oberholser made an 8-footer for birdie.

But a five-shot lead didn't make it any easier for Oberholser, who once called this tournament his fifth major because of so many childhood memories.

The plan was to think of only the next shot, but that became a challenge with such a big lead so early. And his nerves began to show.

Oberholser was standing over a 3-foot par putt on the fifth hole when the grandstand started to leave, and Oberholser backed off and asked them to stand still. Then he missed the putt and slapped his leg. With his the mark of his amateur partner in front of his line, he picked it up before realizing his partner was putting for par.

Uncertain what to do, he replaced the mark and his partner tapped in. Because they were a team, they had to take Oberholser's bogey for the pro-am competition, and wound up one shot behind.

He steadied himself with a birdie on the par-5 sixth and then kept his comfortable lead because Weir continued to struggle with his putting and no one else managed to make a run. Sabbatini reached 13 under, but missed the ninth fairway to make bogey and fell seven shots behind.

"After nine holes, I realized my chances were dead," Sabbatini said.

Divots: Singh made an eagle on the 18th hole for a 68, matching the low round of the day. He tied for seventh.

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