Former Socceroo striker John Aloisi claimed a goal four minutes into the second half after his mis-hit shot rolled towards the line as Coyne moved in for a desperate clearance.

The ball travelled off Coyne's boot, over the line and through a hole in the side netting, with referee Beath stunning Sydney players by awarding a corner and not a goal.

But after a heated protest led by Aloisi, Beath consulted his linesman on the eastern touchline before overturning the decision and awarding the goal.

It gave Sydney a 2-1 lead until Perth equalised in the 79th minute before Aloisi struck for a second time three minutes from time to steal all three points to keep his team alive in the Premiership race.

While conceding Aloisi's first goal had gone in, both cach Dave Mitchell and skipper Chris Coyne were convinced Beath was swayed by either a replay or advice relayed via a match official through the referee's earpiece.

"It was a goal - there was no question it wasn't a goal - but I think it'd been decided it was a corner and I think they've showed it on the big screen and everyone's 'oh, it was a goal'," Mitchell said.

"I think they changed their mind. The linesman didn't indicate it was a goal at the time and the referee's gone the same ... he's changed his mind.

"I'm not complaining. It's disappointing that he's changed his mind and I didn't think he was right to do it."

Coyne added: "Of course I did (see the ball go in). I tried a bit of 'kidology'. I thought it was one of them that we got away with.

"We didn't start moaning to the referee afterwards. We were disappointed with the decision because we weren't aware of the fact that you can change decisions through technology.

"It's something I'm a big fan of and a big believer in, but until it's there for anyone to see, I think the decision should have stood because there's no way they've changed their mind on anything other than watching the big screen or maybe the earpieces that they're now wearing."

Aloisi was in no doubt he had scored.

"I couldn't believe the referee didn't see it but the referee did really well because he said he would check with the linesman and the linesman obviously saw it," he said.

"We were showing him the hole in the net ... luckily they got the decision right because it helped us."

It was a massive call in the context of the season.

The win enabled Sydney (45 points) to leapfrog Gold Coast (44) and keep the heat on league leader Melbourne (47), which visits the SFS next Sunday for what will be a colossal clash between the two bitter rivals.

Coach Vitezslav Lavicka admitted his heart-rate was pushed through the roof as Sydney twice squandered leads before finally burying a weakened but gutsy Perth with Aloisi's winner in the 87th minute.

"It was an amazing game. We have shown the right character because we needed to win and keep the three points this game and we did," he said.

Mitchell said of his team, robbed of six team regulars: "I'm very proud. It's a credit to them.

"They gave everything in the second half and deserved something from the game but unfortunately it wasn't to be. It was a good learning curve for sone of the youngsters out there who performed well."

"It was very encouraging for the future."