FC Seoul reached the AFC Champions League semi-finals for the first time by eliminating Al Ahli, but there was heartbreak for plucky Thai outfit Buriram United.
Montenegrin striker Dejan Damjanovic's 89th-minute strike was enough to settle a scrappy 1-0 win for FC Seoul over Saudi Arabia's Al Ahli for a 2-1 victory on aggregate.
FC Seoul have twice crashed out in the quarter-finals, although they were runners-up in the last edition of the tournament's precursor, the Asian Club Championship, in 2002.
Meanwhile Buriram sent their fans into a frenzy at a packed Thunder Castle Stadium when Spanish defender Osmar Barba scored in the first half against Esteghlal, levelling the tie at 1-1 after last month's 1-0 loss.
But Hanif Omranzadeh nodded home a far-post header to put Esteghlal back on top, before Andranik Teymourian made it 2-1 on the night and 3-1 on aggregate with a thunderbolt in stoppage time.
In Seoul, the hosts repeatedly threatened from dead-ball situations in the first half and defender Kim Jin-Kyu set the tone when he headed over from an early corner. Captain Ha Dae-Sung fired a free-kick straight at goalkeeper Abdullah Al Muaiouf, who was then fully extended by a long shot from Colombian Mauricio Molina.
Mustafa Al Bassas thrashed a powerful strike into the side-netting in one of the best moments from Al Ahli, last year's runners-up, before Molina and Kim Ju-Young both headed over. Korea Republic international Cha Du-Ri, who earlier took a boot to the face, had the closest moment of the opening half when his looping header over Al Muaiouf bounced back off the crossbar.
In a tense second period at Seoul World Cup Stadium, Yun Il-Lok's flick header sailed just wide and Taiseer Al Jassam stung the fingers of home goalkeeper Kim Yong-Dae from distance.
But it was Damjanovic who clinched it in the 89th minute when he was set free in the box and took full advantage, despite a poorly hit shot, as the ball bounced clumsily into the net.
Iranians break Thai hearts
Over in Thailand, Esteghlal threatened in the first five minutes through Teymourian's snap-shot, but it was Buriram who had the better of the first half at their heaving home stadium.
And the hosts' hard work paid off eight minutes from time when centre-back Osmar rose unmarked at a corner and planted a downward header which levelled the tie 1-1 on aggregate.
However, Esteghlal came alive in the second half and there was no surprise when they grabbed the vital away goal on 53 minutes, when Teymourian's stabbed cross was met at the far post by Omranzadeh.
And in injury time, Iranian international Teymourian stole the show when he dispossessed Buriram's Theerathon Bunmathan in a central position and buried a scorching shot from fully 30 yards.
The defeat ends a glorious run by the willing Thai outfit, despite going through three managers during their campaign, as they tried to emulate BEC Tero Sasana's run to the inaugural final in 2003.
Lippi's charges in command
Later, tournament favourites and Chinese double-holders Guangzhou Evergrande, coached by Marcello Lippi, take a 2-0 advantage from the first leg into their away game against Qatar's Lekhwiya.
And Japanese Emperor's Cup holders Kashiwa Reysol are locked at 1-1 with Saudi Arabians Al Shabab ahead of the second leg in Riyadh.