Olsen made a clean start from pole position in his SSR Performance Porsche to lead the field after lap 1, while Mercedes driver Lucas Auer got the jump on Thomas Preining on the run up to Eau Rouge.
Auer kept the pressure up on Olsen for the entirety of the first stint, keeping the gap under a second with a series of fastest laps.
On lap 8 Auer rolled the dice by coming into the pits for his mandatory stop, but his attempted undercut backfired when the Winward crew fumbled his tyre change, costing him at least three seconds.
This meant that Olsen could come into the pits the following lap and still come out in the net lead, while Auer was forced to repass both Laurens Vanthoor and Maximilian Gotz when they made their respective stops later in the race.
Olsen was well clear of Auer when his Mercedes suffered a sudden puncture exiting Eau Rouge, forcing the Austrian driver to peel into the pits and retire.
After Auer's retirement, it was his Winward teammate Gotz who emerged as Olsen's closest challenger and managed to close within a second of the Norwegian with four laps to go, as a sudden bout of rain in the first sector threw a spanner in the works.
The rain, however, subsided quickly and Olsen was able to hang on to the top spot by just 0.818s, clinching Porsche's second-ever victory in the DTM following Preining's triumph at the Norisring in July.
Second place nevertheless marked a first podium finish of the season for reigning champion Gotz, whose previous best result of 2022 was a fourth at the Nurburgring.
Preining made it two Porsches on the rostrum after successfully recovering from a major tank slapper at Raidillon on the opening lap that had dropped him to ninth.
Three-time DTM champion Rene Rast made a sluggish start from ninth on the grid and fell to 10th place, but recovered lost ground by going long in the first stint, climbing up to fourth at the finish.
Rast's Abt Audi teammate Kelvin van der Linde finished a strong fifth, while Team Rosberg's Nico Muller made it three cars from the Ingolstadt-based marque inside the top six.
Red Bull driver Felipe Fraga was classified seventh in the lead AF Corse Ferrari, while Grasser Lamborghini's Mirko Bortolotti charged from 20th on the grid to finish eighth, making most of his moves in tricky conditions in the final laps of the race.
Walkenhorst BMW's Marco Wittmann followed Bortolotti after his own poor qualifying, moving up to ninth on the final lap after overtaking the likes of Nick Cassidy and David Schumacher.
Cassidy eventually picked up the final point in 10th in the Red Bull-backed AF Corse Ferrari, while Schumacher just held off championship leader Sheldon van der Linde - who had qualified down in 22nd - for 11th at the flag.
With just five races to go, Schubert BMW driver van der Linde continues to lead the championship on 110 points, with Rast now level with Bortolotti on 93 points.
Auer would have moved up to 103 points had he not retired from the race while running in second.
Race results:
| Pos | Driver | Car | Gap |
|---|---|---|---|
| 1 | Dennis Olsen | Porsche | |
| 2 | Maximilian Götz | Mercedes | 0.818 |
| 3 | Thomas Preining | Porsche | 6.972 |
| 4 | Rene Rast | Audi | 16.127 |
| 5 | Kelvin van der Linde | Audi | 20.772 |
| 6 | Nico Müller | Audi | 21.102 |
| 7 | Felipe Fraga | Ferrari | 22.504 |
| 8 | Mirko Bortolotti | Lamborghini | 27.636 |
| 9 | Marco Wittmann | BMW | 29.319 |
| 10 | Nick Cassidy | Ferrari | 29.996 |
| 11 | David Schumacher | Mercedes | 31.116 |
| 12 | Sheldon van der Linde | BMW | 31.174 |
| 13 | Esteban Muth | BMW | 31.420 |
| 14 | Arjun Maini | Mercedes | 31.666 |
| 15 | Luca Stolz | Mercedes | 32.540 |
| 16 | Maximilian Buhk | Mercedes | 32.817 |
| 17 | Marius Zug | Audi | 35.696 |
| 18 | Ricardo Feller | Audi | 35.803 |
| 19 | Rolf Ineichen | Lamborghini | 59.316 |
| 20 | Alessio Deledda | Lamborghini | 1'28.293 |
| 21 | Dev Gore | Audi | 2'07.883 |
| 22 | Clemens Schmid | Lamborghini | 1 lap |
| Mikael Grenier | Mercedes | Retirement | |
| Lucas Auer | Mercedes | Retirement | |
| Maro Engel | Mercedes | Retirement | |
| Laurens Vanthoor | Porsche | Retirement | |
| Philipp Eng | BMW | Retirement |
