The Wanderers looked to be heading for a comfortable if unadventurous win at Commbank Stadium on Saturday courtesy of a Jack Hingert own goal in the first half against a 10-man Roar outfit.
But the game was flipped on its head when Margush attempted to stop a clumsy touch in his own penalty box from going out for a corner in the 89th minute.
Brisbane's Alex Parsons, who had a goal chalked off for a narrow offside a few minutes earlier, chased after the ball and Margush lost his composure.
He brought Parsons to ground with a textbook rugby tackle and was shown a straight red by referee Jack Morgan with Jay O'Shea slotting the penalty past substitute goalkeeper Tomas Mejias.
"It was tough to take, it's disappointing clearly," a dejected Rudan said.
"We need to get around Daniel - we all make mistakes.
"It's unfortunate that we couldn't see the game out and pick up all three points.
"I'm sure he knows what happens but we need to make sure he's in a good head space."
The Wanderers had high hopes of making a late run towards the finals places but the draw leaves such an outcome incredibly unlikely.
"It makes it tougher," Rudan added.
"We keep fighting all the way to the end and that's just the way it has to be."
Rudan's side survived an early scare when Brisbane's Cyrus Demhie flashed a shot across goal in the opening 90 seconds.
The Wanderers started sluggishly but found their groove when James Troisi delivered a no-look pass into Jack Rodwell in the Roar box in the 41st minute.
The Englishman crossed and, under the pressure of Bernie Ibini, Hingert turned the ball into his own net.
Brisbane coach Warren Moon suffered further blows with Luke Ivanovic skying a gilt-edged chance over Margush's bar and saw captain Tom Aldred sent off for a second yellow card when he felled Rodwell with 20 minutes to go.
The Roar didn't die wondering and after Parsons chased a ball into the box, Margush struggled to control it and brought the Brisbane man to ground.
O'Shea slotted past Mejias as Moon expressed his delight at his side's spirit.
"It was symptomatic of him and the other boys in how they wanted to press on and work even with 10 men," Moon said.
"They had the lead and a numerical superiority for large parts of the second half but I don't think we were troubled too much.
"That's how I want us to play where we don't stop running."
