Hale Irwin, the Champions Tour's all-time wins leader, parred the final five holes of his round to finish at 14-under-par 274. Tom Watson (68) and Tom McKnight (71) ended two strokes further back at minus-12.
The 51-year-old came right back with a birdie on the sixth. He made it two in a row when his birdie putt on seventh at TPC of Michigan found the bottom of the cup.
Jacobsen moved to 12 under with a birdie at the par-4 11th. He then birdied the par-5 13th. Jacobsen ran in a birdie putt from off the green at the 16th to get into a tie for the lead at 14 under.
He came right back with a birdie on 17 to move one clear of Irwin. Jacobsen two-putted for par on the last and watched as Irwin did the same. Jacobsen now owns two wins on the Champions Tour, both in major championships.
'I'm very proud of that,' said Jacobsen of having won two majors in his brief Champions Tour career. 'I've been playing fairly well. This was my first chance to play here at the Senior Players Championship and the TPC is a great golf course. It's a tricky golf course.'
Irwin got off to a hot start with birdies on the first and third. He climbed to minus-15 with a birdie on the par-5 seventh.
Around the turn, Irwin stumbled to a bogey on the 10th and another on No. 12. He got one stroke back with a birdie on No. 13, but closed with five straight pars to end one stroke short of Jacobsen after a round of 2-under 70.
D.A. Weibring fired a 7-under 65 to move to 10-under-par 278. He was joined there by Gil Morgan, Larry Nelson, second-round leader Dana Quigley, Allen Doyle and Gary McCord.
David Eger, Morris Hatalsky, Gary Koch, Bruce Lietzke and Mark McNulty ended one stroke further back at minus-9.