Craig Stadler posted a 5-under-par 66 to take second place at the Champions fourth major of the season. Jay Haas, like Jacobson a Champions Tour rookie, played well as he posted a 4-under-par 67.
Jacobson moved into red figures with a two-putt birdie at the par-5 fourth. He came back with birdie at the sixth as he dropped a 7-iron within 20 feet of the cup.
The 50-year-old knocked a sand-wedge to 5 feet at the par-5 eighth to setup birdie No. 3. However, he stumbled to a three-putt bogey at the par-4 ninth as he made the turn at minus-2.
Jacobson's second to the par-4 12th came to rest 10 feet from the cup. He rolled in that birdie try and came right back to birdie the 13th.
He kept his hot putter rolling as he drained a 20-foot birdie try at the 15th. After laying up at the 17th, he hit his third shot to the par-5 to 20 feet and sank that putt to get to minus-6.
'I had hip surgery a couple of months ago,' Jacobson said. 'Hitting the ball is no problem, but actually walking 18 holes has been quite difficult, the difficult part for me on the rehab. I have been doing all my stretches and everything, but I can't tell you how much improved I am this week over last week.'
Jacobson has completed just two events this year. The last one was the Long Island Classic at the beginning of July. Since then, the recovery from his surgery has hindered him.
'I told my wife and my caddie starting off, I'm going to go as many holes as I can. I walked, I did a lot of stretching,' Jacobson said. 'I'm simply in the middle of my rehab, and coming back from being on crutches for five or six weeks I have to learn how to walk again. All the muscles in my leg atrophied. This is a huge boost for me health-wise.'
Stadler got on the board with a birdie at he 13th, his fourth. He came right back with a 4-foot birdie putt at the next two make it two straight.
The Walrus, as Stadler is known, rolled in his third birdie at the 17th. He again made it back-to-back birdies as drained a 40-footer at the 18th to make the turn at minus-4.
Stadler opened the front nine with five consecutive pars. He dropped a 7-iron within 12 feet at the par-3 sixth to pick up his fifth birdie. He parred his final three holes to cap a bogey-free round of 66.
'I played well. I had last week off, which was a good week,' said a relaxed Stadler. 'I had some things I had to tend to and didn't get over across to the British. It's probably a good thing. I've played just a ton of golf the last few months and was really in need of some time off. I took the week off and enjoyed it. I hit my irons horrible all week, and all of a sudden today I get it straightened out.'
Wayne Levi, Mark McNulty, Gil Morgan, Jose Maria Canizares, David Eger, Bob Gilder and 2002 U.S. Senior Open champion Don Pooley share fourth place at 3-under-par 68.
Bruce Fleisher, the 2001 U.S. Senior Open champion, heads a group of players at minus-2. Also in that group are Jay Sigel, Tom Kite, Leonard Thompson, Tom Jenkins, Darrell Kestner, John Aubrey, Andy Bean, Walter Hall and Dan Halldorson.
Bruce Lietzke, the defending champion, struggled in the first round of his title defense. He posted a 4-over-par 75 and stands in a tie for 75th.
Pete Oakley, the unheralded club professional who won the Senior British Open last week, opened with a 5-over-par 76.