The semi-finals are decided and while the top four have affirmed their league placings so far, it's a miraculous achievement for Adelaide nonetheless.

They'll now face another near impossible task in a semi-final against Perth Glory, but since the Reds and Marco Kurz announced their impending split, Adelaide have been a team on a mission.

It took until the 118th minute after both sides had chances to win, Craig Goodwin delivering the ball to Baba Diawara, who controlled, held and distributed out wide to Halloran.

The Aussie striker - who hit the post with a cracking curler in the first half - made no mistake in slotting past the glancing glove of Eugene Galekovic at his near post.

"It was like gladiators at the end, a pretty dramatic ending I've got to say," Halloran said.

"You know what a game is like at the end of 120 minutes - I think it was Baba who passed it to me but I'm not even sure.

"It's the culture we've built at the club over the past couple of seasons, the boys never shirk our efforts, especially with the crowd behind us, it's just a great night."

Goodwin took the time to praise Diawara's brief cameo and the striker's role at the club.

"It was just one of those moments on the counter after Kitto played it up, Baba did brilliantly to hold it up and turn and Halloran offered an excellent finish," Goodwin said.

"It shows what Baba can do, holding the ball and playing a calm final ball. It took 120 minutes, there have been two hard-fought games before this."

Adelaide legend-turned-City star keeper Galekovic proved a slight villain in the end, unable to keep out an effort he probably should have saved after a night of jeers and taunts from the Red Army behind him.

"Both teams had a few chances, probably deserved to go to penalties to be honest," the subdued keeper said.

"Credit to Adelaide, they were good the way they pressed, but to deal with this is pretty hard. You obviously focus on the game but as the minutes go and there's the chance of penalties you think about it. 

"It's a disappointing season, we had a team that we thought could win something and we didn't."