Geelong's GMHBA Stadium has become the scene of a chaotic A-League classic, with Steven Lustica the hero as Western United overcame Perth Glory in a 5-4 goal fest.

United snatched the lead through Victor Sanchez after just 10 minutes, before the teams traded eight goals in the space of half an hour in an enthralling second half - with United youngster Dylan Pierias and Perth's Carlo Armiento each scoring a brace.

"It's gonna take a bit of time to calm down from that one," United coach Mark Rudan said.

"You don't coach many nine-goal thrillers and for it to have see-sawed the way it did ... all I can say is I'm glad that we're on the right end of those goals."

The home team made their early dominance count when Connor Pain squared the ball to Lustica, who cleverly left it for Sanchez to curl a delightful shot into the top corner.

During the week, Rudan had demanded more from skipper Alessandro Diamanti and the Johnny Warren Medallist responded, returning to his captivating best as United's midfield outhustled their Perth opponents.

Glory boss Richard Garcia switched out Daniel Stynes for Armiento after just 38 minutes, then swung another two changes at the break.

Then, Uruguayan Bruno Fornaroli sparked the contest to life.

The Glory marksman shuffled on the ball then laid it off for Armiento to fire home from an angle in the 56th minute.

Two minutes later, Armiento repaid the favour, cutting the ball back for Fornaroli to cheekily back-heel the Glory in front.

In response to the goal, Rudan made three changes, bringing on Pierias, Lachie Wales and Brendan Hamill in one move.

They paid off immediately when Wales burst down the left wing and lifted a cross over the Glory defence for Pierias to head home on 60 minutes.

Four minutes later, the young attacker - who hadn't scored in his previous 26 appearances - controlled Tomoki Imai's cross, outmuscled his opponents and smashed home his second to regain the lead.

Perth responded in the 69th minute when skipper Neil Kilkenny floated a free kick to the back post, where Nicholas D'Agostino snuck in to head home.

In the 75th, United regained their lead when Wales whipped a ball across the face of goal, with Imai pouncing at the far post.

"At 4-3 I turned to Richard Garcia and I said 'this is crazy," Rudan said.

Three minutes later, Armiento snared his brace when he reacted quickest at a free kick, drilling home a spilt ball to level the scores again.

But it would be United who had the last say in the 84th.

After a pack of players met Diamanti's corner, the ball spilled out to Lustica, whose shot took a deflection and rattled home to hand United their first win of the campaign.

"It was a crazy game - I thought we did well to get ourselves to where we wanted to be in the second half," Garcia said.

"The little things that we did wrong came from our fatigue so we've got to improve on that."