An effervescent performance by playmaker Vassilis Spanoulis steered Olympiacos to a 68-64 victory versus 2010 champions Barcelona while Andrei Kirilenko overcame early jitters to help CSKA Moscow beat holders Panathinaikos Athens 66-64.
Taunted and vastly outnumbered by noisy Panathinaikos fans throughout both semi-finals, their bitter city foes donning the red and white colours of Olympiacos had the last laugh as Spanoulis led the charge for their team against Barcelona.
With the clock ticking in a nail-biting finish, he buried a three-pointer and then dished a no-look pass to Richard Dorsey for an easy lay-up as Olympiacos got sweet revenge for an 86-68 defeat by Barcelona in the 2010 final.
"Vassilis is a real team leader and one of a kind, he will always take responsibility at crunch time and attack the basket to take the pressure of his team mates," Olympiacos's Macedonia centre Pero Antic told Reuters.
"We now have a great chance to prove wrong everyone who wrote off this team before the season started and win our first major trophy since 1997.
"It would be no more than our (Serbian) coach Dusan Ivkovic deserved after once again showing immense experience and tactical prowess second to none," said Antic.
Since they won the elusive double of the Euroleague and the Greek league 15 years ago, Olympiacos have played second fiddle to Panathinaikos in both competitions and arrived at the Final Four in Istanbul as the least fancied team.
Spanoulis, who joined Olympiacos from their arch rivals in 2010 after winning the Euroleague with Panathinaikos the season before, outplayed Barcelona's much heralded shooting guard Juan Carlos Navarro and finished with a game-high 21 points.
His inspired display was matched in the day's opening semi-final by Kirilenko, who endured a torrid opening before he demonstrated the skills of a former NBA stalwart to propel CSKA into Sunday's final with 17 points and nine rebounds.
Panathinaikos looked the more likely winners after storming to a 29-15 lead at the end fo the first period but paid the price for setting Euroleague's worst record for points in a quarter in the Final Four, scoring five in the second period.
The Greek outfit's advantage was reduced to 34-32 by halftime and they couldn't stop a rejuvenated Kirilenko nailing one crucial shot after another in CSKA's patient second-half comeback.
"We had problems in defending their pick-and-roll offence early on and were not focused enough in the first quarter but all the pieces came together when we applied our trademark half-court pressure," CSKA centre Nenad Krstic told Reuters.
"Sunday's final will be the biggest game of my career and we now have to recover both emotionally and physically from this roller coaster which could have gone the other way and deservedly so had Panathinaikos scored on their last possession.
"The luckier team won but you have to earn your luck and we earned ours because we never gave up although we were in disarray and looked lost in the opening period," he said.
Barcelona will play Panathinaikos in the third-place match on Sunday before CSKA and Olympiacos lock horns in the final.