Dortmund’s late arrival meant kick-off was delayed by 10 minutes, although the opening to the game was hardly worth the wait as a blocked Kevin Stöger effort was the only shot in the early exchanges.
Meanwhile, the first shot on target came 20 minutes in when Joe Scally struck the ball sweetly from the edge of the box, but Gregor Kobel was equal to it between the BVB sticks. Five minutes later, Kobel was beaten by an excellent Nico Elvedi volley from a free-kick, but no one was surprised to see the offside flag go up immediately.
With safety not quite confirmed, Die Fohlen kept the pressure on, yet they struggled to break through as Haris Tabakovic had a close-range effort thwarted by Kobel after more good work from Scally.
The hosts were inches away from a deserved lead a couple of minutes before the break when Franck Honorat’s corner was headed a whisker wide by Yannik Engelhardt before the visitors finally gave Moritz Nicolas something to do with the final kick of the half, although a tame Samuele Inacio effort summed up Dortmund’s attacking output.
Gladbach began the second half where they left off, with Tabakovic missing from six yards out when under pressure and Stöger shooting straight at Kobel from a good position, but a half chance for Julian Brandt suggested there was better to come from Die Schwarzgelben in the second 45 minutes.
Still, it wasn’t until a wild Julian Ryerson strike midway through the half that they next had any sort of effort at goal.
Niko Kovac threw on Fabio Silva to be the difference-maker, and he orchestrated a counter-attack with 12 minutes to play, but couldn’t produce the finish the move deserved.
Five minutes from time, a low centre from Honorat was begging to be turned in, but Rocco Reitz just couldn’t get the angles right with his side-footer. Reitz, though, soon played an important role in the 90th-minute winner, threading a ball through for Tabakovic to beat Kobel with a cool finish.
Although the offside flag initially denied him, VAR confirmed he had timed his run to perfection, handing Gladbach victory, survival and a first H2H win in seven. UEFA Champions League-bound Dortmund, meanwhile, have now lost back-to-back away games for the first time in 16 months as their season ends in a whimper.