Norbert Meier opted for just one alteration to his side from their last outing before the international break as Sven Schipplock was replaced by Antonio-Mirko Colak.
Maik Walpurgis, in charge of Ingolstadt for the first time, immediately tamped his authority on the team by making four changes. Tobias Levels, Romain Brègerie, Stefan Lex, Lukas Hinterseer all dropped out as Florian Haderdjonaj, Marcel Tisserand, Anthony Jung and Hartmann earned starting berths.
Both sides have their chances
After the initial concern surrounding Marvin Matip and Hadergjonaj had subsided, the game soon came to life with both sides going close to opening the scoring.
The first chance fell for Hartmann, who collected a poor back pass from Aytac Sulu. The defender could only watch on and hope that Michael Esser came up trumps, and the former VfL Bochum stopper did just that with an important save. Darmstadt replied through Änis Ben-Hatira's free-kick, which cannoned back out off the bar.
Ingolstadt had multiple chances to make their very physical presence count from set-pieces in the first period yet couldn't make the most of the opportunities when they arose. Not even Pascal Groß' delivery could pick apart the stubborn home defence, who were keen to make the Schanzer's wait for a win continue.
Hartmann hammers home
Despite the best efforts of both sides to get a goal before the break proving unsuccessful, they continued to come forward in search of the all-important opener.
Darmstadt were the team making the early second half running and had two glorious chances to put the game beyond any reasonable doubt. The pair came from two tanalising, low crosses from Marcel Heller, although Colak and Ben-Hatira somehow managed to slide the ball wide on each occasion.
It was not immediate, although the Lilies would pay for their inability to finish as Ingolstadt went ahead in incredible fashion. A long ball forward was met by Sulu, only to loop up in the air and fell onto the right foot of Hartmann. He sent a superb, dipping volley past the outstretched hand of Esser and into the top corner.
The home side willed their side towards an equaliser but couldn't find a way past Martin Hansen, who produced telling saves late on, especially from Heller's volley. Esser even made a late run into the box but his goal-bound shot was blocked, in what was a much-needed result for the visitors. A missed chance for Darmstadt, however.