Poppy Hills is one of three courses in the rotation. Pebble Beach Golf Links and SpyGlass Hill Golf Course also host over the first three rounds, while Pebble Beach hosts Sunday's final round.
Luke Donald, who tied the course record at SpyGlass on Thursday, struggled in the second round. He only managed an even-par 72 at Pebble Beach and is tied for third place with Jonathan Byrd (65) and Fredrik Jacobson (67), both of whom also played Pebble Beach on Friday. The trio is knotted at 10-under-par 134.
Weir, who has not finished outside the top four in the last three years here, opened on the back nine Friday with a birdie at the par-5 10th. He played inconsistently from there as he battled a rolling fog, a steep drop in temperature and some swing problems. The Canadian mixed two bogeys and two birdies the rest of the back nine to make the turn at 1-under-par 35.
Weir did not get off to a great start on his second nine because he faced an 8-footer for par at his 10th. He drained that putt, then hit a 6-iron to 8 feet to set up birdie at the second.
'That really kind of propelled me, got me going,' admitted Weir, who also posted top-10 finishes in 2000 and 2001. 'Today for the first six, seven holes was nice, then the fog rolled in.'
He parred his next four holes, but found a fairway bunker on the left side with his drive at the seventh. Weir hit an 8-iron from 150 yards out to 6 feet and converted the birdie try.
It certainly did not look like Weir was going to make birdie at the eighth. He hit a solid drive, but his wedge spun back to 50 feet. No matter to the former Masters winner as his putt, which traveled through the fringe, found the bottom of the cup.
'It was just a lucky shot,' said Weir. 'Kind of a fluke.'
Weir hit another strong drive at the par-5 ninth, then hit an even better 3-wood to 25 feet. His putt narrowly missed left, but Weir tapped in for birdie and a four-shot lead.
'I want to keep moving forward,' said Weir. 'I expect to play well tomorrow. I've been close and this tournament has been good to me. It would be nice to win.'
Weir endured one of his worst seasons on tour last year, but it came with good reason. He battled a neck injury which saw him to dip to 56th on the tour money list.
'I don't feel I've gone anywhere,' admitted Weir. 'I just wasn't healthy last year. You just can't play against these players out here when you are not at full strength, especially a guy with my game, where I rely on preciseness and hitting fairways.'
Oberholser collected two birdies and a bogey over his first four holes. His next birdie came at 11, and he came back to birdie the 12th. Oberholser, who has back-to-back top sixes the last two years, traded a birdie and a bogey at 15 and 16, but birdied 18 to move into sole possession of second place.
Nick Watney carded a 1-under 71 at Poppy Hills and fell into a tie for sixth place. Davis Love III (67), Mark Wilson (68), Greg Chalmers (70) and Michael Allen (71) all posted their second rounds at Pebble Beach and joined Watney at 8-under-par 136.
Defending champion Phil Mickelson did not play well en route to a 2-over 74 at SpyGlass on Friday. He is part of a group tied for 52nd place at minus-3.