Oberholser only managed a final-round, even-par 72 to finish at 17-under-par 271, but it was good for a five-shot win.
'To win at Pebble Beach in front of the home fans is awesome,' acknowledged Oberholser. 'The greens were firming up and fast. I was hanging on for dear life a little bit on the back nine. I'm glad I could get into the house.'
Rory Sabbatini actually came in second place after a two-under 70. He posted a 12-under-par 276 total at Pebble Beach Golf Links.
Weir, who shared the 54-hole lead with Oberholser, struggled badly on Sunday. He shot a 6-over 78 and tied for third place with Jonathan Byrd, who carded a 3-under 69. The duo finished at minus-11.
The two third-round co-leaders were knotted at 17 under par, but it did not take long for Oberholser to take command. At the par-five second hole, Weir, the 2003 Masters winner, hit his second shot out of bounds. He knocked his fourth shot into a greenside bunker and blasted out to 11 feet. Weir missed the bogey putt, and Oberholser got up and down for birdie from a different trap. The three-shot swing put Oberholser in firm command of the lead.
He extended it at the next hole, although Weir assisted in giving Oberholser a bigger cushion. At the par-4 third, Oberholser ran home a 9-foot birdie putt, while Weir missed the fairway off the tee and walked off with a bogey. In three holes, the duo went from a tie for the lead, to Oberholser standing on the fourth tee with a five-stroke margin.
'My wedge game and my putting was what killed me,' admitted Weir, who blamed mud on his ball for the errant second at No. 2. 'I putted poorly. When you hit 13 out of 14 fairways and shoot 78, your wedge game and putting is usually not very good.'
Oberholser gave one back at the fifth hole when he missed a 6-footer for par. Both players birdied the par-5 sixth when Oberholser sank a 4-footer and Weir played his third shot inside a foot. At the short, par-3 seventh, Weir hit a poor shot to 34 feet. He missed the birdie try, but left himself with 4 feet for par. The Canadian did not convert the par putt to fall back. Oberholser had a good chance to further distance himself from his fellow 54-hole leader, but pulled a 10-foot birdie putt.
The duo parred eight, although Oberholser sweated his par out thanks to a poor drive and a second shot that bounced through the green. He hit a delicate chip to 16 inches and tapped in for par. Oberholser did not have the same luck at the ninth when his drive found a fairway bunker. He laid up short of the green, but came up short of the putting surface with his third as well. Oberholser chipped to six feet and holed the bogey putt to claim a four-shot lead at the turn.
Weir sealed the victory for Oberholser with his play on the first two holes of the back nine. He three-putted from slightly over 40 feet at the 10th, then hit a terrible approach to No. 11. Weir landed in a greenside bunker and could not save par from 9 feet.
Oberholser, now armed with a six-shot lead, stumbled at 13. He found a bunker down the left side, then came up short with his 9-iron approach. He hit his third to six feet, but missed the putt and dropped to minus-17. The par-5 14th was not kind to Oberholser as he found rough off the tee, then again with his second. He left the hole with back-to-back bogeys, but still held a four-shot edge since Weir and Sabbatini did not make any move.
Oberholser bounced back at 15 in an unlikely fashion. His drive bounced off the cart path twice, hopped into a tree before falling into the rough. The 31- year-old wedged his second to seven feet and rolled in the birdie try, while Weir missed a 5-footer for par. That bogey dipped Weir to 11-under par, one shot behind Sabbatini.
At the par-3 17th, Oberholser found a bunker off the tee and blasted out 20 feet past the hole. He nailed the par-saver, then played 18 conservatively en route to a par and the win.
'It's really nice,' said Oberholser, who shared the 54-hole lead here two years ago, but struggled to a final-round 76 and a tie for fourth place. 'It's a stepping stone and hopefully I continue to get better.'
Craig Barlow (69) and Daniel Chopra (71) shared fifth place at minus-10. Vijay Singh (68), American Ryder Cup captain Tom Lehman (70), Brian Davis (73), Luke Donald (74) and Nick Watney (73) tied for seventh place at 9-under-par 279. Phil Mickelson, who won this title in 2005, only shot a 5-over 77 and finished in a tie for 38th place at minus-3.