Postecoglou ended Spurs' 17-year wait for a major trophy with that win over Manchester United - and was rewarded with the sack.
He is now at Nottingham Forest, and their trophy drought is twice as long at 35 years. But it is not that 1990 Football League Cup win that Forest fans are recalling as they prepare for the club's visit to Seville to play Real Betis.
Forest are two-time kings of Europe, winning the European Cup (now Champions League) in 1979 and 1980 under the charismatic managerial genius Brian Clough, and the memories still burn brightly.
But this will be their first Continental tie in 10,781 days, since a UEFA Cup quarter-final against Bayern Munich in March 1996.
Asked if it feels like a big moment for the club, the Australian said: "Oh absolutely. Without a shadow of a doubt.
"Thirty years, a club that's absolutely climbed to the peak of European football in the past and you can just imagine how the supporters are feeling.
"There's probably a couple of generations in there who've heard the stories but not lived the experiences. Now they can live their own experiences."
For Postecoglou himself the campaign is a title defence and he added: "I'm excited by it. When I made the decision to accept the position, it was one of the most enticing bits."
Forest will be cheered on by 3,385 travelling fans at the cavernous La Cartuja in Seville, where Betis are playing while their Estadio Benito Villamarin is redeveloped.
Postecoglou is in the early stages of transforming Forest from the safety-first football practised by his predecessor Nuno Espirito Santo to the attacking style he is known for.
He is yet to win a match after two defeats and a draw, all away from home, since taking over earlier this month.
While the team transitions he recognises he may have to compromise, in Europe at least.
"It's fair to say that the world is crying out for me to be pragmatic," he said. "But I'm just not built that way.
"I've always said what I like to do and what I enjoy more than anything is winning, so whatever it takes we'll do.
"In the final we [Tottenham] had to play a certain way because of the availability of the players we had.
"I think you do have to approach the Europa League a little bit differently.
"Tactically, there's some tweaks you need to make to allow the players to perform at their best. I still want to win every game."
Real Betis midfielder Giovani Lo Celso, who played under Postecoglou at Spurs, praised the Australian.
"Obviously he is a great coach," the Argentina international said. "He is a coach that likes the best kind of football."
Betis lost the third-tier Conference League final to Chelsea last season and with Forest are among the Europa League favourites.
Coached by former Real Madrid and Manchester City boss Manuel Pellegrini they have made a mixed start to the Spanish league season with three draws away and two wins and a loss at home.
with PA
