The Bundesliga-bound Bavarian team was looking for its first win in three matches and was gifted an opportunity to open the scoring when a penalty was awarded for Adam Bodzek's challenge on Stefan Lex, a professional foul for which the Fortuna captain was also sent off.
Düsseldorf keeper Michael Rensing saved Alfredo Morales's spot-kick.
Fortuna striker Joel Pohjanpalo opened the scoring for the visitor less than five miunutes later with a calm finish.
Substitute Ingolstadt defender Moritz Hartmann levelled the score on the hour mark, only for Fortuna striker Ihlas Bebou to restore the Rhinelanders' lead.
Ralph Hasenhüttl's men were to have the last laugh, however, as headed efforts from Socceroos star Leckie and Marvin Matip - the latter six minutes into injury time - ensured Ingostadt took another step to promotion to next season's top flight.
With Bundesliga.com
