Jobe, who has never won on the senior tour, had a double-bogey on the par-3 ninth hole before rallying with six consecutive birdies.
''I've been playing well. I just haven't put everything together,'' Jobe said. ''I kind of got of fortunate with my finish.''
Day shot a 67 and made birdie on No. 18 to join Jobe atop the leaderboard
Kevin Sutherland, who shared the first round lead with Day and Langer, the tour's money leader, is at 9-under.
Langer leads a group at 7-under despite getting five birdies in the second round. Langer, who has already made nearly $1.7 million this season, shot a second-round 71.
''I'm four behind, so that's a lot to make up,'' Langer said. ''But it's happened before, so hopefully I will play better.''
Jobe misjudged his approach on the par-3 ninth hole - but he answered for that mistake by tying a tour mark for consecutive birdies this season.
Jobe has just two top-10s this season. But he and Day will be the golfers the rest of the field will be chasing on Sunday.
''I got pretty mad. I actually hit the shot I wanted to hit. It was just absolutely the wrong club. A total misjudge,'' Jobe said of his miscue on No. 9. ''Then I was just like 'Alright, start over.'''
Day, who also hasn't won a senior event, hit 33 of 36 greens in regulation and is the only golfer through two rounds without a bogey.
Langer, who is seeking to become the first senior circuit golfer in seven years to win three consecutive starts, got off to a great start. He holed out from 80 yards on the fourth hole for a par-4 eagle that gave him the lead.
But Langer - who had the second-worst round of his senior career at Wakonda in 2015, when he finished tied for 48th - stumbled with three straight bogeys to close out the front nine. Langer's approach on the par-3 No. 14 then got caught in the wind, stopping it far short of the green, and he had to settle for another bogey.
Lehman, who has been under par following all 11 of his rounds at Wakonda, notched five birdies on the back nine. Lehman has recorded top-10 finishes in all five of his trips to Iowa, but he's never won in the state.
''I hit a lot of really good putts. Typically if you're hitting your line, it tends to build confidence. It's when you start missing your line consistently where you start to lose it,'' Lehman said.
This is just the second PGA Tour Champions event for Flesch, who turned 50 late last month. Flesch, like the rest of the field, will likely have to deal with temperatures in the mid-90s and gusting winds.
''I know I'm going to have to get to at least double digits (Sunday) to have any sort of chance.''
Scott McCarron, who won his first PGA Tour Champions event in Iowa in 2016, is also at 7-under.