Covid-19 rules in Germany had led to a Saturday start and a 54 hole event at Green Eagle Golf Courses as fans returned to fairways in Europe for the first time since October 2019.
The 7,603 yard layout is widely regarded as one of the toughest on Tour but - after starting on the tenth - Detry played the front nine in 29 with seven birdies and a double bogey to get to four under and lead by one shot.
Belgian Detry has been one of the European Tour's most consistent performers since graduating from the European Challenge Tour in 2016 but is still looking for a first victory in his 114th event.
He won the ISPS HANDA Melbourne World Cup of Golf in 2018 alongside Thomas Pieters but has three second place finishes in individual events, including two last season.
The 28-year-old clearly has the game to enter the winner's circle and he was relishing testing it on a set-up that he believes is up there with the toughest in the game.
"The golf course is really tough this week, it’s almost a U.S. Open set up," he said. "I played the front nine really steady, my first nine holes, didn’t really make anything and made a little mistake - a bogey - but on the back nine I got it going.
"Two early birdies, a double on one of the easiest holes, then I had a nice bounce back with a tap-in birdie and had another four birdies.
It’s very Major. I played the US PGA two weeks ago and it’s a similar approach, you have to drive it on the fairway otherwise it's really penalising
"It’s completely different, it’s very Major. I played the US PGA two weeks ago and it’s a similar approach, you have to drive it on the fairway otherwise it's really penalising.
"In a way that’s golf that suits me a bit more, I tend to struggle on easy courses where you’re forced to make birdies otherwise you’re losing ground and it’s a completely different approach on this golf course.
"I’m very pleased with the way I’ve been playing. I hit 12 fairways today, some really good golf so I’m pleased with it and I’m looking forward to the next couple of days."
Detry turned in one over after a poor tee shot brought a bogey on the 16th but his second nine was a very different story.
He holed from the fringe on the first and made a 13 footer on the second and, while he made a double on the next after finding the water and three putting, he hit back with a stunning approach to the fourth.
A 16 footer on the sixth was followed by a putt from the fringe on the next and he put approaches to around 12 feet on the eighth and ninth to hit the front.
Chesters missed a 13 footer on the last to join the lead after making three birdies, two bogeys and holing out from 109 yards for an eagle on the ninth on a course where he has two top tens.
Wu made four birdies and a bogey from the first group of the day, Björk made four birdies on his second nine after turning in 39 from the tenth, and Law made six birdies and three bogeys.
Frenchman Benjamin Hebert, Scotland's Scott Jamieson, Swede Rikard Karlberg, Dane Benjamin Poke, home favourite Marcel Schneider and England's Matthew Southgate were at two under, with 21 players under par.