The visitors were far too strong at Coopers Stadium on Friday night with the majority of the 14,716 in attendance left disappointed after Auckland picked apart United to win the two-leg tie 4-1 on aggregate.
Auckland coach Steve Corica was immensely proud of his side securing a maiden appearance in the decider, against either Newcastle or Sydney FC.
"I'm very happy obviously; we said it from the start it was going to be a tough place to come here," he said.
"Everyone wrote us off and we perform like that, 3-0 away from home. Everyone performed at a very high level and we're through to the final."
The Reds made a fast start and had a good chance inside the opening few minutes when Jonny Yull whipped in a free kick for Anselmo who was waiting at the back post, but the Brazilian's shot flew across the face of goal.
Anselmo picked up a knock soon after and was replaced by Luka Jovanovic, which turned the tide in the visitors' favour after they had started to work their way back into the game.
On 21 minutes United failed to clear a corner and from the ensuing scramble inside the area, Jesse Randall shot on the turn and struck the upright.
As the interval drew near, Hiroki Sakai drove towards goal down the right and shot powerfully from just inside the area, forcing an impressive save from Joshua Smits.
From the corner, Jake Girdwood-Reich rose highest at the near post and nodded in the perfect in-swinging corner, giving Smits no chance.
In first-half injury time, Yull collected the ball from Ethan Alagich outside the area and almost curled his shot into the bottom corner but it went inches wide.
Adelaide had a fast break on 50 minutes which saw Jovanovic square from Ryan White. The Reds' Player of the Season managed to turn the cross goalbound but it was thwarted by Michael Woud.
Auckland doubled their advantage on 58 minutes thanks to a penalty from Sam Cosgrove. The towering striker was brought down by Panagiotis Kikianis and after a quick check from VAR stepped up to dispatch the spot kick.
Cosgrove slammed it straight down the middle and although Smits managed to get his legs to the shot, it was too powerful and trickled over the line.
The Reds huffed and puffed in search of a way back into the match but the visitors all the answers.
On 86 minutes, Logan Rogerson iced the win after a slick counter attack from Auckland.
Randall tore down the left wing and with United left stranded in defence, shot a cut back across the area for Rogerson to tap in at the far post.
United coach Airton Andrioli said the Reds' end to the season was bittersweet.
"It's sort of a double feeling," he said.
"A sense of being proud of what we've done this year and sort of a sadness or disappointment of getting so close but not crossing over that line to go to a grand final."
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