The visitors otherwise had the opportunity to get off to a dream start after a few minutes of play, but Emilio Simonsen managed to kick a hole in the air with the goal at his mercy. However, after the early warning, the home side grabbed the initiative, enjoyed their best spell in the game, and were rewarded after 21 minutes of play.
Elias Achouri slammed the ball into the box, and Viktor Claesson stole in front of keeper Mattias Lamhauge, who had to see the Swede's clever finish with the outside of his foot slide into the net.
FC Copenhagen were at their best in the first half, but also struggled to turn possession into big goal chances. Therefore, Fredericia could still glimpse a potential surprise at the break.
And the promotion outfit's dream of claiming a point against the favorites was further boosted four minutes after the interval when Gustav Marcussen twisted and turned into the Copenhagen box and was brought down by Munashe Garananga to win a penalty.
Marcussen himself had no trouble converting the big chance to restore parity. But the visitors did not enjoy the momentum for long before Moses Opondo clumsily brought down Mohamed Elyounoussi just six minutes later, and Youssoufa Moukoko converted the penalty even though Fredericia keeper Mattias Lamhauge wasn't far from saving the attempt.
Junnosuke Suzuki then seemed to have put the game beyond doubt when he made it 3-1 in the 78th minute with a sneaky finish from the edge of the area, but Fredericia refused to give up.
Soon after, Oscar Buch reduced the deficit after a counter-attack, and nervous tension simmered in the Parken Stadium until the very last whistle.