Halloran broke the deadlock on 21 minutes after a helter skelter opening against Victorian NPL powerhouse Bentleigh Greens at Kingston Heath on Friday night.
Jordan Elsey doubled the advantage in the 49th minute to ensure a 2-0 win, a fourth straight cleansheet and back-to-back finals appearances.
And, for the South Australians, a chance for redemption after falling 2-1 in extra time to Sydney FC in last year's decider.
“We were fortunate to score an early goal in the second half to kill it off but credit to Bentleigh they pushed us all the way," Halloran told Fox Sports post-match.
“It was back and forth – we really didn’t too well to get control of the game and there really wasn’t much of a midfield, just going back and forth.
"I’m just happy to get the win and looking forward to the final now."
For Bentleigh - second time semi-finalists - it was the first time they conceded in this Cup run and only the fourth time they failed to score in 2018.
The result means the competition will again be decided between two A-League outfits. Western Sydney Wanderers and Sydney will battle it out tomorrow night to see who will face off against the inaugural champions.
For Halloran it was a fruitful return to action in Australia after five years abroad. The fringe Socceroo and 2014 World Cup veteran left V-Varen Nagasaki after five games in July.
Coach Marco Kurz has big wraps on the 26-year-old who didn't disappoint, and might have scored a brace but for a top save in the 31st minute.
Halloran has made it clear he's ambitious for his first piece of silverware. Back in August he said: “To date, I’m yet to win any silverware so I definitely have ambitions of coming to Adelaide to win something and to win the FFA Cup would be a great start."
After a long pre-season he's itching to get into the season proper.
"Everyone’s ready to kick things off. There’s no substitute for competitive matches," he said.
"I’m loving it (being back in Australia). "We've got a great bunch of boys here, they’re pretty down to earth and you can’t beat the Aussie camaraderie."