Western Sydney Wanderers hung on for a 1-0 victory at ANZ Stadium on Saturday night to break their crosstown rivals’ 19-game unbeaten start to the season.

But the result might have been different had Sydney FC been awarded a stoppage time penalty after skipper Alex Brosque was brought down in the box by Robbie Cornthwaite.

The whistleblower is understood to have offered an apology after seeing a replay of the incident, according to media reports.

Sydney believe they were denied at least one other penalty for an earlier foul on Milos Ninkovic.

Brosque said he spoke to Beath about the Cornthwaite challenge after the match.

"I was very frustrated and annoyed at the fact he missed it, because I felt he was close enough," he said.

"There was contact, it was loud enough – there was enough sound to hear there was contact and really there was no need to go down, that was my frustration.

"He just said he didn't really see it, and neither of his assistants were in a good enough position to see it."

But the Sky Blues talisman remains confident the league leaders won’t dwell on their derby disappointment.

The derby result was their first loss to Wanderers since January 2014.

“It’s a good test to be honest,” Brosque told Fox Sports.

“The reality is we’ve lost one game all season.

“For (Wanderers), they’ve needed something this year and they got a good win so good on them.

“But we’ll just keep doing what we’ve been doing all year (which is) playing well. We’ll pick ourselves up for Melbourne City and get three points over there.”

Despite downplaying the defeat, Brosque believes it’s misguided to think the maiden loss is beneficial before the Finals Series.

“I don’t agree with that saying. I think if you carry on winning, or not losing, you’re doing well,” he said

“Unfortunately tonight a couple of decisions didn’t go our way, but we’ve had some go for us previously, so we live with what happened tonight.

“We will bounce back, have a good week at training and go down for a big one in Melbourne.”