Darmstadt put five past Köln to pile pressure on Gerhard Struber
The only change in 1. FC Köln's team ahead of the Darmstadt tie was Rasmus Carstensen stepping in at right-back for Max Finkgräfe.
For Darmstadt, Florian Kohfeldt made one change as Sergio López came in for Guillermo Bueno in defence.
Starting for the first time in seven months, Carstensen was shaky to begin with as Killian Corredor was allowed plenty of space on his side. In the ninth minute, Darmstadt showed their early spurts of pressure as Isac Lidberg narrowly dragged a shot wide of the post.
However, just two minutes later Fraser Hornby finished a relatively simple chance in the bottom corner to put the Lillies 1-0 up.
With the away side putting on more pressure, they almost equalised through Timo Hübers just on the half hour mark.
Eight minutes afterwards, the equaliser came through a Tim Lemperle tap-in from a Linton Maina cross. Despite this, the score did not last long at all as Darmstadt responded in the 40th with Hornby's second after Lidberg set him up.
In the second half, Köln never really got going and were stifled by the efficiency of Darmstadt's scoring.
During the 54th minute, a poorly positioned high defensive line for Köln allowed Darmstadt to counter effectively and Isac Lidberg finally got his goal.
Despite a double substitution in bringing on Jan Thielmann and Dominique Heintz, Köln's defence remained shaky as ever as their high line got caught out once again as Philipp Förster netted the Lillies' fourth.
Entering the final part of the game, Köln enjoyed individual dribbles by Denis Huseinbašić and Linton Maina around the opponent's box but this was to no avail.
Finally, one last dagger was sent through the heart of Gerhard Struber's side as Darmstadt centre half Aleksandar Vukotić netted from a free-kick.
This result means that Gerhard Struber is in even more pressure for his job as coach of Köln and it also distances Köln further from the conversation for promotion.
For Darmstadt, this win signals the start of a new era under Florian Kohfeldt and provides them a two-point cushion out of the bottom three.