Stenson, who shared the lead after the first round of the US Open a week ago, faded to a tie for 27th and memorably compared the greens at Chambers Bay to like “putting on broccoli”.
But the former European number one found the putting surfaces at Eichenried Golf Club more to his liking as he overcame a triple bogey with eight birdies to finish five under par, two shots behind leaders Lasse Jensen, Rafael Cabrera-Bello and Daniel Gaunt.
Starting on the back nine, Stenson made an ideal start with birdies on the 11th and 12th, but then contrived to take seven on the 319-yard 16th when his approach spun back off the green into a water hazard.
The 39-year-old bounced back with a birdie on the 18th and picked up another shot on the first before surging through the field with four birdies in succession from the fifth.
Another birdie looked on the cards following a perfect drive on the par-five ninth, but Stenson pulled his approach left of the green and saw it bounce off a cart path and into a hospitality tent.
“I was in a good position to finish with five in a row, but I think the wind switched a little bit and I was in between clubs and went with the longer club and ended up way in the grandstand,” Stenson said.
“It would have felt really nice to finish with a birdie on nine to make nine birdies and a triple to shoot six under, but eight birdies and a triple isn’t too bad either.
“Potentially there were some thoughts about the airport after I made a triple on the 16th without doing too much wrong, but I came to my senses and started playing some golf afterwards. I guess the patience practice at the US Open was paying off.
“The greens are soft but they are rolling nicely and as good as they have ever been in Munich.”
Cabrera-Bello has finished fourth, 13th and second in his last three events, but let good chances to win a third European Tour title slip from his grasp in the Irish Open and Lyoness Open.
“I’ve been playing well for a few weeks now and did so again today,” said the 31-year-old Spaniard, who fired nine birdies and two bogeys in his 65. “I putted really nicely and holed a few good long ones so it was nice to keep the momentum going after a week off.
“The set-up and the atmosphere in this tournament is very, very special and it’s only Thursday; it felt like a weekend almost with really big crowds out there. It’s nice and it helps you get in the zone and it worked for me today.”
Jansen carded seven birdies in a flawless round while Gaunt, a two-time winner on the Challenge Tour, birdied his first three holes and added five more against a solitary bogey.
“When you get off to a good start like that, it kick-starts your day,” Gaunt said. “All I wanted to do was just keep progressing from there and chase down the leaders, really.
“I hit a great shot into the ninth and to finish with a really good putt again was the icing on the cake today.”
England’s Andrew Johnston was a shot off the pace on six under with compatriot Tommy Fleetwood alongside Stenson on five under.
“I got out of jail a lot,” Fleetwood told Sky Sports 4. “I played poorly for a lot of it and when I hit my tee shot on the third [his 12th hole] into the jungle it was really not looking like a five-under-par day.”
After scrambling a bogey on the third, Fleetwood promptly birdied the next, holed from 15 feet for an eagle on the sixth and birdied the ninth, adding: “I finished strongly and hit some decent shots coming in but it was a struggle all day and rounds like that are great when you get something out of them.”
Home favourite and 2008 champion Martin Kaymer had to settle for a level-par 72 which at least featured an unlikely birdie on the ninth, when he pitched from the edge of a pond to six feet after his approach had bounced out of the trees.