Adelaide United weathered an attempted fightback by Western Sydney on Thursday night to triumph 2-1 in extra time and advance to the semifinals of the Australia Cup.

Cutting inside and letting fly with a sizzling long-range effort, Austin Ayoubi had the hosts ahead after just nine minutes of play on Thursday evening.

The home side failed to capitalise on a series of chances, and their lead was erased by the Wanderers' Nicolas Milanovic in the 68th minute.

Extra time would ultimately be needed, but the scores were only level for three minutes of it, with Ryan Kitto bursting into the box and firing Adelaide into a lead they would not relinquish.

Earlier, with Dylan Pierias causing his former side problems, the hosts fashioned a series of opportunities to double their advantage across the opening stanza, but failed to get past Tristan Vidackovic, with Zach Clough and Kitto also both hitting the crossbar.

And with the visitors staying in the game and testing Adelaide keeper James Delianov on either side of the break, parity was restored when Marcus Antonsson knocked a Jack Clisby cross down for Milanovic to fire home.

With Wanderers defender Anthony Pantazopoulos forced off with an injury, both sides exchanged chances as the game wore on, Adelaide's Luka Jovanovic and Ryan White squandering two late opportunities to win the game.

Kitto spared the youngsters' blushes, when Clough lifted a ball over the defence for the Reds skipper, who casually shook off Aidan Simmons before firing the three-time Australia Cup champions through.

The Reds will now face the winners of Saturday's quarterfinal between NPL Queensland outfit Moreton City Excelsior and A-League giants Melbourne Victory, with a spot in the final on the line.

On Wednesday, NPL Victoria table-toppers South Melbourne punched their ticket to the semifinals after coming from behind to defeat local rivals Hume City 3-2 in extra time, with Jordon Lampard heading home the match-winner in the 115th minute.

Max Mikkola and Harrison Sawyer also got on the scoresheet for South.

It is the second time the former NSL powers have reached the semi-finals in the 10-year history of the modern Australia Cup, having previously reached the final four in 1965 and 1966 in the competition's first incarnation.

AAP