Both teams ended the regular season in shaky form, with Adelaide finishing third and Wellington sixth, but they now know that they are potentially only three games away from Grand Final glory.
Match preview
Adelaide will have to do things the hard way if they are to be crowned A-League champions for only the second time, and the first since 2016.
A direct route into the post-season semi-finals seemed almost secure for much of the run-in to the campaign, only for a dreadful dip in form at the worst possible time to condemn them to the Elimination Final.
Carl Veart's men took only two points from the last 12 on offer to them, including a 4-1 home defeat to Central Coast Mariners on the final day of the regular season - a result which saw them leapfrogged by their conquerors into second place.
Indeed, Adelaide were unbeaten in 12 matches prior to suffering two defeats in their last three outings, with the exception in that time being a madcap 4-4 draw with Perth Glory which saw three goals scored in stoppage time, Perth turning a 3-2 deficit into a 4-3 lead before Adelaide remarkably rescued a point with a 99th-minute equaliser.
Worryingly for The Reds, both of their defeats came at Coopers Stadium too - an uncharacteristic slump considering they had lost just once in front of their own fans for more than a year before that.
Adelaide do boast a formidable record at home to Friday's opponents, though, with Wellington winning just one of their last 10 visits and Adelaide winning both of the last two by four-goal margins.
That includes a 5-1 victory when the Phoenix last came to Coopers in March, although the visitors perversely led that match in a number of metrics and will feel that the scoreline heavily flattered their hosts.
A repeat of that performance, if not the scoreline, could raise hopes of an upset on Friday, then, and Wellington do come into the game on the back of victory in their final regular-season game.
That 1-0 triumph over Macarthur last weekend ended a five-game winless streak which included four defeats and saw them pick up just one point from 15 on offer, putting their place in the Finals for a second successive season under serious threat.
The Nix failed to make it past this stage last year and have not reached the semi-finals since 2011-12, so ending that 11-year wait would make for a perfect parting gift to manager Ufuk Talay.
Talay will leave the club at the end of his contract this summer to be replaced by his assistant Giancarlo Italiano, making this series his last shot at leading the New Zealand outfit to their first-ever major trophy having fallen at this stage twice before.
There is no doubt that they go into the match as underdogs, though, while the all-time head-to-head record between the two sides also leans in favour of the hosts, who have won 19 of the 43 meetings to Wellington's 11.
Adelaide United Australian A-League form:
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Wellington Phoenix Australian A-League form:
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Team News
Adelaide have been handed a trio of fitness boosts for this crucial encounter, with Veart welcoming three players back in timely fashion.
Hiroshi Ibusuki, Zach Clough and Jay Barnett all missed the costly defeat to Central Coast on the final day of the regular season, but will be available for this match.
Nick Ansell also comes into the squad for the hosts, with Jonny Yull and Bernardo missing out, the latter through illness.
The Reds are still without Harry van der Saag (knee), Josh Cavallo (Achilles) and Juane (leg) through injury.
Veart must also decide whether to unleash the highly-rated 17-year-old Nestory Irankunda, who has made his mark with five goals off the bench throughout the campaign but is yet to start an A-League match.
Wellington will still be without midfielder Ben Old for this match due to injury, while centre-back Nikko Boxall will also miss out having been struck down by illness.
Those are the only two absentees for the visitors, though, with top-scorer and newly-crowned Wellington Player of the Year Oskar Zawada fit to lead the line having missed the last meeting between the two sides.
The experience of Kosta Barbarouses could also prove to be important, with the forward having won the A-League four times with three different clubs and scored seven goals in the Finals before.
Adelaide United possible starting lineup:
Gauci; Lopez, Barr, Warland, Kitto; Isaias, D'Arrigo; Halloran, Clough, Goodwin; Ibusuki
Wellington Phoenix possible starting lineup:
Sail; Elliot, Wootton, Payne, Mauragis; Sasse, Rufer, Ugarkovic, Barbarouses; Zawada, Ball
We say: Adelaide United 3-2 Wellington Phoenix
These two sides posted the worst defensive records in the top six, shipping 91 goals between them throughout the regular season, and with plenty of attacking talent for both teams, that could result in a high-scoring affair.
The presence of Zawada in particular will make Wellington believe that they can pull off an upset, but they are underdogs for a reason and we are backing Adelaide to just about come out on top and progress to the semi-finals.