City is now one win away from becoming the first team to complete consecutive A-League Men premiership-championship doubles.

Maclaren's 92nd-minute goal capped off a dramatic second-leg comeback and tees up the first all-Victorian ALM decider against Western United at AAMI Park on Saturday.

It will be City's third consecutive grand final appearance.

Scores were locked at 0-0 after Wednesday's first leg in Adelaide and Zach Clough's wonderful 48th-minute dink put the Reds in front at AAMI Park, before Marco Tilio equalised in the 74th minute to take the game to extra time.

It was City's first victory over a top-four team from 11 attempts this season.

The first half was largely defined by big saves from Adelaide goalkeeper Joe Gauci and City counterpart Tom Glover.

Then, three minutes after half-time, Javi Lopez found Clough, who took a touch with his left foot then coolly chipped a looping, dipping volley over Glover's head.

Adelaide almost doubled its lead in the 57th minute, when Kusini Yengi beat Curtis Good and attempted to finish from a tight angle, only for Connor Metcalfe to clear it over the bar.

Patrick Kisnorbo turned to Tilio off the bench in the 58th minute and 16 minutes later, the Socceroo delivered.

Andrew Nabbout floated in a cross and it went over the head of a leaping Mathew Leckie, but Tilio burst in at the back stick and headed home off the post.

In the 84th minute, Tilio charged forward and let rip with a cracking long-range effort, forcing a brilliant diving save from Gauci.

Yengi attempted to tee up Bernardo in the 90th minute but the young substitute could not get a shot on target.

Two minutes into extra time, Maclaren held up the ball for Metcalfe and while Michael Jakobsen got in the way of the midfielder's shot, he did not properly clear it.

The shallow clearance fell straight to Maclaren, who buried his 16th goal of the season at the near post to seal the grand final berth and condemn Adelaide to back-to-back semi-final exits.