Fredrik Sjovold's 52nd-minute strike secured a 1-0 victory for Bodo/Glimt over Borussia Dortmund in the Champions League on Wednesday, extending the Norwegian side's remarkable home record against Europe's elite.
Bodo were a cut above the 2024 Champions League runners-up and took the lead through Sjovold just after the break.
Dortmund improved in the final half hour but were unable to strike back, despite a late chance for Felix Nmecha.
"There's nothing we can complain about, we deserved to lose," Dortmund coach Niko Kovac told DAZN.
"We didn't bring enough passion today – that's something Bodo did much better. They took the lead and after that we woke up, but by then it was too late."
Dortmund join Manchester City, Inter Milan and Sporting as recent big-name scalps on the artificial turf of Bodo's Aspmyra stadium.
"Each of us needs to ask ourselves what the problem was," Dortmund captain Waldemar Anton said.
"In several areas we were missing our intensity today and without this intensity you won't win a game."
Bodo's run to the round of 16 last season was underpinned by an excellent record at their 8 200-capacity home, officially the smallest venue in this year's competition.
Dortmund arrived in the Arctic Circle on a seven-game unbeaten run but struggled to get a foothold.
The hosts were far more comfortable in the opening half, with Sondre Fet and Ole Blomberg inches away from scoring.
Bodo continued their domination after halftime and broke through when Sjovold turned a low Sondre Auklend cross in at the near post.
Dortmund's level improved after Kovac made four changes on the hour mark, with substitute Nmecha forcing a fingertip save from goalkeeper Nikita Haikin moments later.
The Germans upped the pressure in the dying stages but failed to find a way through as they fell to a first defeat this campaign since the season-opening German Super Cup.