Melbourne Victory kept its season alive for another week and condemned Sydney to finals defeat in the most dramatic fashion with a stoppage time volley from Brazilian Gui Finkler, whose goal gave the hosts a 2-1 win.
Both sides were preparing for extra time and a potential penalty shootout when the excellent James Troisi summoned the energy for a last gasp burst into the Sydney penalty area. His cross was blocked, but the ball fell to Adama Traore, whose chipped pass into the penalty area was met perfectly by Finkler to shatter the Sky Blues' finals dreams in the 91st minute.
It was a suitably thrilling conclusion to an exciting contest in which both sides, at different times, had looked the most likely victors.
Melbourne began this game like a team that wanted to have its qualification for the semi-finals wrapped up in the first 15 minutes, so high was its tempo and so energetic was its approach.
Victory simply monopolised possession in the opening period, playing neat one-twos, working in triangles, probing backwards, forwards, sideways and with patience until they could find the right angle for the defence-splitting pass.
Sydney barely touched the ball inside the first 10 minutes as its hosts made all the running.
It was hardly a surprise. The last time Sydney travelled south for a league match a few weeks ago the Sky Blues had put the game into lockdown, conceding territory and possession to strike with purpose on the break. It worked well on that occasion, with Frank Farina's team going home with a point.
But finals are a different kettle of fish – or so it seemed, and Victory got the lead it deserved in the 19th minute. It was a goal of quality featuring two of the team's key men, Troisi and Thompson, the eventual scorer.
But the move began in defence, when Pablo Contreras, the former Chilean international, stepped forward to rob Alessandro Del Piero, Sydney's playmaker, and play a pass through to Troisi.
The latter – whose hot form in the second half of the season has given him a real chance of selection in Ange Postecoglou's squad for Brazil, slotted through to Thompson, who curled a measured shot round Vedran Janjetovic to beat him inside his left post.
The former Socceroo striker had missed the win over Guangzhou as he had to attend the funeral of his brother-in-law early in the week, so his celebratory point to the sky was a poignant reminder that for all its highs and lows, this is still a game and not a matter of life and death.
At that stage it would have seemed certain that Victory could add to its score at any moment and virtually ensure a semi-final next week.
But Farina's men have proved obdurate and cussed on more than one occasion this season.
A goal down, their counter-attacking strategy had to change. They didn't so much throw caution to the wind, but they too began to play with more attacking purpose and got their reward in the 34th minute with a goal that caught Victory napping.
Victory failed to clear their lines properly and the fall fell to Del Piero on the edge of the box. The Italian legend might be barely able to break out of a walk these days, but his footballing vision is still 20-20. He fed the ball out wide to Ali Abbas, whose cross was met with a first time shot by Sydney full-back Seb Ryall, scoring for the third time against his former team.
What had looked like an uneven contest now became an end-to-end thriller as Sydney, like a boxer who has taken a few rounds of a championship decider to warm up, began to match its hosts.
Although Melbourne at one stage forced five corners in a row it was the visitors who came closest to taking the lead, when Garcia's cross was met first time by Del Piero only for the Italian's drive to crash off the post to safety.
Sydney began the second half rather as Victory had the first. They looked energised and were only denied a lead just after the restart, thanks to Nathan Coe's fingertips as the Victory goalkeeper tipped over a header from Matthew Jurman that looked a certain goal. The goalkeeper repeated the feat soon after to deflect Joel Chianese's effort to safety to keep his side in the tie.
With time running down it looked as though the Sky Blues were the more likely victors, a mood only confirmed after a lovely attack down the left begun by Del Piero's turn and pass to Abbas, whose cross was fired just wide by Ranko Despotovic.
But it wasn't to be, as Victory now prepares for a sudden death showdown in either Brisbane or West Sydney. The Sky Blues will lick their wounds, wonder what might have been – and ponder the future of coach Frank Farina.
MELBOURNE VICTORY 2 (Thompson 19', Finkler 91') def SYDNEY FC 1 (Ryall 33')
VICTORY: Nathan Coe; Adam Traore, Pablo Contreras, Nick Ansell, Jason Geria (Scott Galloway 67'); Mark Milligan (c), Leigh Broxham (Rashid Mahazi 79'); James Troisi, Gui Finkler (Connor Pain 94'); Kosta Barbarouses, Archie Thompson. Subs: Lawrence Thomas, Jimmy Jeggo. SYDNEY: Vedran Janjetovi; Seb Ryall, Nikola Petkovic, Sasa Ognenovski, Andrew Jurman; Milos Dimitrijevic, Terry Antonis, Alessandro Del Piero (c), Ali Abbas; Joel Chianese (Ranko Despotovic 70'), Richard Garcia. Subs: Ivan Necevski, Aaron Calver, Matt Thompson, Alex Urosevski.
YELLOW CARDS: VICTORY: Contreras 53', Ansell 75'.
REFEREE: Peter Green
CROWD: 20,802 at Etihad Stadium
SATURDAY: ELIMINATION FINAL
Central Coast v Adelaide, Central Coast Stadium, 4.30pm