Engstler had been running a steady third behind polesitter Bortolotti and Mercedes rival Luca Stolz in the first part of the race, but an impressive strategy call from Grasser to pull him into the pits just before a Full Course Yellow elevated him to the lead.
Engstler’s run to victory was made easier by an agonisingly slow pitstop for SSR Performance driver Bortolotti, a problem which also forced team-mate Nicki Thiim out of the race.
At the start of the race, Bortolotti pulled away cleanly from pole position, but Saturday winner Jack Aitken made contact with second-placed Luca Stolz and ran wide into Turn 2.
This dropped the Emil Frey driver towards the middle of the pack, and as he tried to regain ground he collided with the Lamborghini of Maximilian Paul at Turn 3, suffering terminal damage to his Ferrari.
A number of other drivers got caught up in the incident, prompting race control to deploy the safety car before the end of lap 1.
When the action resumed, Bortolotti again led the field in his Lamborghini, with Stolz following him in the Mercedes and Engstler holding third in the Grasser Huracan.
When the pit window opened after 20 minutes of racing, the majority of the front runners opted not to stop immediately, with midfield runners first to blink as they tried to make up positions.
Among the early stoppers were Schubert BMW’s Rene Rast and Emil Frey driver Thierry Vermeulen, who then engaged in a fierce fight for a spot in the lower half of the top 10.
Having lost a position to Rast on the latter’s out-lap, Vermeulen sent his Ferrari down the inside of the triple champion into Turn 3, but the two came to blows at the exit of the corner - with the Dutch driver sent into the barriers as a result of their impact.
Vermeulen was forced to retire from the race on the spot as his Ferrari caught fire, with the race control deploying a Full-Course Yellow to help recover his car.
But before the FCY was activated, both Engstler and Maro Engel had already entered the pits, allowing them to come out in front with a net advantage of 20 seconds.
Early race leader Bortolotti, who was yet to stop at that time, finally pulled into the pitlane after the FCY period was over. But SSR mechanics struggled to change the left-rear tyre on his Lamborghini, with the Italian rider eventually rejoining the track at the bottom of the pack.
This left Engslter and Engel to duel it out for victory, with the two running nose to tail in the final laps of the race.
Engstler eventually held on by just 0.300s to take his maiden victory in the DTM, while HRT duo Stolz and Arjun Maini finished third and fourth behind the sister Mercedes of Engel.
Abt Sportsline driver Ricardo Feller looked set to finish fifth but his Audi driver began to slow down at the final corner, with the German dropping to ninth by the time he crossed the finish line at crawling speeds.
The chief beneficiary of Feller’s late drama was team-mate Kelvin van der Linde, who led brother Sheldon across the line in fifth.
The Schubert BMW driver had dropped to 19th and last after having to slow down on the opening lap to avoid the collision between Aitken and Paul, but the decision to pit at the first opportunity propelled him to sixth at the finish.
Seventh place went to his team-mate Rast, who was lucky to avoid serious damage on his car after his incident with the other Emil Frey car of Vermeulen.
Grasser driver Christian Engelhart recovered from a penalty for speeding in the pitlane to take eight, ahead of the hobbled Audi of Feller.
Marco Wittmann took the chequered flag in 10th, as all three BMWs finished inside the top 10.
Behind, Lucas Auer was able to drag his Winward Mercedes to 11th, despite losing a heavy chunk of the front bodywork from his car in the first-lap crash between Aitken and Paul.
It was another low-key day for Porsche as reigning champion Thomas Preining could only salvage 13th place, one spot ahead of Manthey EMA team-mate Ayhancan Guven.
Bortolotti picked up the final point in 15th after losing a huge chunk of time in the pits.
| Cla | Driver | Car / Engine | Delay |
| 1 | Luca Engstler | Lamborghini | |
| 2 | Maro Engel | Mercedes | 0.300 |
| 3 | Luca Stolz | Mercedes | 18.325 |
| 4 | Arjun Maini | Mercedes | 20.554 |
| 5 | K.van der Linde | Audi | 32.981 |
| 6 | S.van der Linde | BMW | 35.217 |
| 7 | René Rast | BMW | 39.364 |
| 8 | C.Engelhart | Lamborghini | 39.874 |
| 9 | Ricardo Feller | Audi | 43.730 |
| 10 | Marco Wittmann | BMW | 53.667 |
| 11 | Lucas Auer | Mercedes | 1'00.010 |
| 12 | Clemens Schmid | McLaren | 1'01.397 |
| 13 | Thomas Preining | Porsche | 1'01.708 |
| 14 | Ayhancan Guven | Porsche | 1'02.066 |
| 15 | Mirko Bortolotti | Lamborghini | 1'02.419 |
| 16 | Ben Dörr | McLaren | 1'14.177 |
| - | Maximilian Paul | Lamborghini | |
| - | T.Vermeulen | Ferrari | |
| - | Nicki Thiim | Lamborghini | |
| - | Jack Aitken | Ferrari |
