Weir shot his 69 at the Spyglass Hill Golf Course, while Oberholser carded his 66 at Pebble Beach Golf Links. Poppy Hills Golf Course was the third course in the rotation, but Sunday's final round will be staged at Pebble Beach.
Luke Donald, the first-round leader, shot a 1-under 71 at Poppy Hills on Saturday. He is alone in third place at 11-under-par 205.
Harrison Frazar posted a 5-under 67 at Poppy Hills and shares fourth place with Nick Watney (70), Rory Sabbatini (68) and Brian Davis (68), all of whom teed it up at SpyGlass. The group is knotted at 10-under-par 206.
Weir played poorly early in his round as he traded a pair of birdies and a pair of bogeys in his first seven holes. The 2003 Masters champion looked destined to drop another shot to par at nine, but a great pitch from in front of the green saved his par.
The Canadian birdied 11, 14 and 18 to join Oberholser in a share of the lead.
Sunday could be a major step for the left-hander. Weir battled through a neck injury through much of 2005, dropping to 56th on the PGA Tour money list. He has not won since the 2004 Nissan Open.
Oberholser, who is winless on the PGA Tour, but collected two victories on the Nationwide Tour in 2002, opened on the back nine at Pebble Beach, and collected his first birdie at the 13th hole.
He notched his second birdie at the 17th, then rolled in a long birdie putt at the par-5 18th. The 31-year-old made the turn at 3-under-par 33 and caught Weir for first place.
Oberholser stumbled on his first hole of the second nine. He missed a 7- foot par save, but rebounded at the par-5 second. Oberholser knocked his second shot to 22 feet and nearly holed the eagle try. The putt moved left at the end and Oberholser settled for a birdie. He made it back-to-back birdies with a 7-footer at the third to get to 15 under par for the championship.
The middle holes of Pebble Beach's front nine tested Oberholser and the San Jose State University graduate answered the bell. He found the right bunker with his approach at four, but converted a 4-footer to save par. At the par-3 fifth, Oberholser hit his tee ball to 45 feet, but left himself another 4-footer for par. Once again, Oberholser ran home the tester to stay at minus-15.
Oberholser's putter let him down at the par-5 sixth. He went through the green with his second and chipped 5 feet past the cup. Oberholser's putt never flirted with the hole, pulling it left, but he was still tied for the lead with Weir, who birdied the 11th at SpyGlass.
Oberholser distanced himself from Weir at the seventh. He sank a 21-foot birdie putt at the seventh, then snaked in a left-to-right birdie putt from 25 feet at eight to reach minus-17.
He nearly fumbled his last hole, despite a 320-yard drive at the ninth. He had 166 yards to the hole and hammered his approach over the green. Oberholser chipped to 5 feet and holed the par putt to keep his share of the 54-hole lead.
Oberholser has a tremendous record at this event with a tie for sixth last year and a share of fourth in 2004. He shared the 54-hole lead in 2004 with Vijay Singh, but shot a 76 in the final round.
'I wasn't very comfortable. I had a 'deer in the headlights' thing going,' admitted Oberholser, who lost in a playoff at the 2004 Wachovia Championship. 'I felt like I needed to play him mano-a-mano and it didn't work out too well.'
Mark Wilson shot a 1-under 71 on Saturday at Poppy Hills. He is tied for eighth place with two players who competed at SpyGlass in round three - Tim Clark (70) and Daniel Chopra (69). The trio finished 54 holes at 9-under- par 207.
Defending champion Phil Mickelson will need serious help if he is to make it two in a row. He carded a 5-under 67 at Pebble Beach and is part of a group tied for 11th at minus-8