Spanoulis, nicknamed "Kill Bill", buried 22 second-half points to steer recession-hit Olympiakos to a memorable 100-88 win against the eight-time Euroleague winners at London's 02 Arena on Sunday.
As so often before in his illustrious career, which has included one title in Europe's premier club basketball competition during two stints with bitter city foes Panathinaikos and a spell with the Houston Rockets, the 30-year-old stepped up to the mark when his team needed him most.
"It was an unbelievable three days in London because we came as champions but also as outsiders, considering the budget and the difficult season in which we've had to play so many games," Spanoulis told reporters after engineering his team's fightback from a 17-point deficit.
"We had our backs against the wall so many times but this team has amazing chemistry. Everyone knows his role, we feel like a family and we are a family.
"We came into a difficult situation but remained united in the locker room and we deserve to be at the top of Europe," he said.
Olympiakos, cheered on by thousands of Greek fans, became only the fourth team in the competition's history to retain the title and their comeback was just as impressive as last year's when they beat CSKA Moscow 62-61 in the final thanks to a game-winning shot on the buzzer by forward Georgios Printezis.
Their double success is all the more admirable given that it came amid the crippling recession in Greece, which has had three years of harsh budget and wage cuts with unemployment rising to 27 percent.
Olympiakos, like other sports clubs, have felt the crunch and were forced to release some of the game's big names in order to stay afloat, including NBA stalwart Josh Childress in 2010 and Serbia guard Milos Teodosic in 2011.
Olympiakos triumphed last year after overturning a 19-point second-half deficit in the final but repeating the feat this term looked unlikely when their towering American center Joey Dorsey left the club midway through the season after the holders endured a patchy run.
Driven by Spanoulis and the supporting cast, notably Printezis, fellow forward Kostas Papanikolau and American center Kyle Hynes, Olympiakos reached the playoffs and then the Final Four with a 3-2 win over Efes Istanbul in a gruelling quarter-final series.
Coach Georgios Bartzokas had a huge pair of shoes to fill after taking over from Serbian Dusan Ivkovic during the off-season but kept the bulk of the side together, preserving the team spirit that enabled Olympiakos to yet again humble the royalty of European club basketball.
"We were united and we are a big example for all of Greece that we can make miracles," Bartzokas said.
"Life makes beautiful stories and I want to thank the fans who came here all the way from Greece and spent so much money. I was in the right place at the right time with this team."
Bartzokas, who coached modest Greek sides Panionios and Maroussi before he succeeded Ivkovic, paid tribute to his predecessor and fellow Serbian Zeljko Obradovic, who won 11 Greek championships and five Euroleague titles with Panathinaikos before he quit last year.
"The Serbian coaches who achieved previous titles with Greek teams helped Greek basketball. They brought the knowledge. But my face is the face of a Greek coach. I hope there is a continuation and that many coaches will achieve more titles."
(Writing by Zoran Milosavljevic in Belgrade; additional reporting by Patrick Graham and Michael Szabo in London; Editing by Clare Fallon)