D.A. Weibring carded his third consecutive 3-under 69 to take fourth place at 9-under-par 207 in the season's fifth and final major on the South Course at The Reserve Vineyards & Golf Club.
A trio of former winners of this event are one stroke further back at minus-8. Tom Kite, the 2000 Tradition winner, is joined at 8 under by 2001 champion Doug Tewell, as well as 1997 and 1998 winner Gil Morgan. They are joined there Craig Stadler, who carded a double-eagle at the par-5 16th.
Jacobsen, a University of Oregon graduate, is the hometown favorite as his firm runs this event. After he parred the first three holes, Jacobsen caught fire and it looked as though he would run away from the field.
He dropped in a birdie at the par-4 fourth and came right back to birdie the fifth. Jacobsen then drained a 4-foot birdie try at the eighth to jump to 12 under.
Jacobsen, who won the U.S. Senior Open four weeks ago, parred the seventh, then missed his first green in regulation since the first round at No. 8. Including the eighth, he missed four straight greens, but played those holes in 1 under.
He got up-and-down for par at the eighth, ninth and 10th. Then at the par-3 11th, he missed the green left, but holed his chip shot for birdie to get to 13 under.
Jacobsen then missed several birdie chances on the way to the clubhouse. He narrowly missed a couple of putts before stumbling to a bogey at the 17th, his first since bogeying the same hole in round one. He missed another makable birdie putt at the last to share the overnight lead with Fernandez.
'I hit some really good putts coming in,' said Jacobsen, who is making just his fourth start on the Champions Tour. 'I had a chance pretty much on every hole to make a putt and when things don't go your way, you've just got to stay positive and keep rolling them. I left a couple right in the heart.
'I'm rolling the ball well as I said the last two days. You can't make every putt, but if you put a good roll on it, then something is going to go in. So, hopefully tomorrow I'll make the ones I'm not supposed to make.'
Fernandez, one of three first round co-leaders, quietly moved back to the top of the leaderboard. He opened with a 5-foot birdie at the first and came back with a birdie at the fourth to move to 8 under.
The 58-year-old Fernandez dropped in his third birdie at the ninth, his third in three days at that hole. He rolled in a 5-footer for birdie at the 12th to get to 10 under overall.
The Argentine maintained his hot play with a birdie at the par-3 14th. Fernandez cruised to three straight pars, as he headed to the last within one of the lead.
Fernandez, a four-time winner on the Champions Tour, dropped his third shot within 6 feet of the cup at the last. He rolled in that birdie try to join Jacobsen in the lead.
'I struck the ball very well again today,' said Fernandez, who has battled neck and back pain all weekend. 'I holed a few more putts and that was the difference. Putting was definitely the difference for me today.'
The two leaders share the lead in greens hit in regulation through three rounds. Both Fernandez and Jacobsen have hit 45-of-54 greens in regulation this week.
Bruce Lietzke, the 2003 U.S. Senior Open champion, stands alone in ninth place at 7-under-par 209 after a 1-over 73. Andy Bean, John Bland, Jose Maria Canizares, Tom Jenkins, Jerry Pate and Dave Stockton are one stroke further back at minus-6.
Tom Watson, the 2003 Tradition champion, climbed into a tie for 21st at 4-under-par 212 after a 4-under 68.