The 60-year-old Haas, the 2005 and 2009 champion, had an eagle and seven birdies on the first 14 holes at Rock Barn Golf and Spa's Champions Course, dropped a stroke on the par-4 15th and closed with three pars.
Still, it was Haas' best single round this season on the 50-and-over tour. It also extended his streak of sub-par rounds in Champions Tour events to 21.
''I had a great start,'' said Haas, who won the last of his 16 Champions Tour titles in June 2012 in Des Moines, Iowa. ''It was pretty magical. I played well all day, expect for the bogey where I three-putted. But overall, I couldn't be happier.
''I've been playing well, and still playing well from earlier in the year. I drove the ball well, my irons were good and my putting was good today. It was nice to make those putts, and to get off to that start.''
The 50-year-old Durant - who teed off on the back nine - rebounded from bogeys on Nos. 14 and No. 17 to shoot a 7-under 28 over his final nine holes.
That equaled the tournament record for a nine-hole stretch, first set in 2011, and the Champions Tour mark for lowest nine-hole score this season.
Durant went on to finish with eight birdies and an eagle, and posted his lowest round since joining the tour in April.
''I'd have a good birdie, then I'd three-putt the next hole,'' said Durant, a four-time winner on the PGA Tour. ''I kept giving (the birdies) right back. But I was fortunate to make a birdie on No. 18 to turn (his first nine holes) at 1 under.
''After that, I felt that I was onto something. I made some good putts. The greens were very receptive, and the ball was rolling good. You could do some stuff out there.''
Langer is skipping the tournament after finishing third last year. He has a tour-high five victories, two of them majors.