FC Copenhagen recorded their third successive win in the Superliga championship playoffs and the biggest so far this season.
FC Copenhagen's German goalkeeper Diant Ramaj played his first derby since three weeks ago where he head-butted Brondby's Thomas Mikkelsen and received a three-game suspension.
However, the heavy pressure he faced did not seem to affect Ramaj, who was one of the main characters before the break.
After just one minute, he saved his team, when Mathias Kvistgaarden was played through after Jacob Neestrup's side had lost possession in midfield.
The visitors seemed somewhat overwhelmed at the start of the match and made a series of mistakes but FC Copenhagen gradually dug themselves back into the match but had problems finding space in Brondby's well-organized rearguard.
In the other end Kvistgaarden was handed a new chance to get on the scoreboard after half an hour, when Benjamin Tahirovic delivered a wonderful through-ball for the Celtic-target Ramaj saved again.
The visitors took the lead a bit out of the blue barely ten minutes before the break. An initially harmless cross from Giorgi Gocholeishvili was flicked on by Thomas Delaney, and in-form Jordan Larsson made no mistake to open the score from close range to score his fourth foal in four games.
The home side began the second half with a much-needed injection of energy and quickly created two good opportunities, but once again Ramaj was up to the task.
Without fans from both camps, the atmosphere never reached the level that usually characterizes a derby between the two top teams.
And the home crowd was silenced again, when Victor Froholdt hammered the ball into the roof of the net after 63 minutes to make it 2-0.
With barely a quarter of an hour to go, the Brondby-defense caved in again when Brazilian Gabriel Pereira popped up at the back post to triple the lead.