By Gabriel TanFollow @@gabetan13
The only goal of the game at the Azadi Stadium came after just two minutes in rather fortuitous circumstances after Khosro Heydari shaped up to cross down the right wing, but ended up sending the ball in off the far post.
But despite doing enough to claim the lead ahead of the return encounter on September 18, the Iranian giants are likely to be concerned with the way their less-illustrious opponents more than matched them throughout the 90 minutes.
However, they will have no complaints about the way they started as they took the lead in the second minute; Heydari finding space down the right and mishitting a cross that ended up sailing over a hapless Sivaruck Tedsungnoen and into the top corner.
Although the blow of falling behind so early on could easily have deflated a lesser team, Buriram remain undeterred and remarkably began to enjoy the better of the proceedings.
In the 14th minute, they could have had a penalty after Suree Sukha's blistering effort appeared to hit the hand of a defender inside the area, but the referee was unmoved, much to the chagrin of the Thai outfit.
As the half wore on, the visitors continued to look dangerous but were just unable to create a clear-cut opening to test the opposition keeper, and they could have fallen further behind in the 63rd minute.
Racing onto a great pass by Javad Nekounam, Fardin Abedini was left in space inside the box but Pratum Chuthong weighted in with a vital challenge just as the Esteghlal substitute was about to pull the trigger.
A minute later, the Thunder Castle really threatened for the first time when Jesus Berrocal met a left-wing cross at the far post and sent a firm header towards goal, but Mehdi Rahmati covered his angles well to make a smart reflex save.
Rahmati was called into action once more eight minutes later when he recovered well to punch a loose ball clear before Bruno Herrera could pounce, after the Iran international had initially flapped at a Jirawat Makarom cross.
Nonetheless, as much as Buriram were beginning to look the likelier to score, the hosts were also dangerous in their forays forward and Heydari came excruciatingly close to grabbing a second in the 76th minute; trying his luck from the edge of the area with a ferocious drive that sailed inches over.
As the game entered its closing stages, there was still time for last chance for Buriram to grab an equaliser and - more importantly - a valuable away goal.
That came a minute from time when the excellent Osmar Barba, racing onto a clearance on the edge of the box, proceeded to unleashed a blistering effort that looked destined for the bottom corner until Rahmati reacted brilliantly to tip it wide.
But while they were ultimately unable to force a draw on Wednesday, Buriram's spirited display will give them plenty of confidence that they can overturn the deficit in next month's second leg.
Esteghlal: Mehdi Rahmati, Pejman Montazeri, Hanif Ormanzadeh, Amir Hossein Sadeghi, Hashem Beikzadeh (Fardin Abedini 56'), Javad Nekounam, Jlloyd Samuel, Khosro Heydari, Siavash Akbarpour (Mehdi Nazari 88'), Mohammad Ghazi, Farhad Majidi (Arash Borhani 63').
Buriram United: Sivaruck Tedsungnoen, Suree Sukha, Chitipat Tanklang, Osmar Barba, Tanasak Srisai (Anawin Jujeen 75'), Pratum Chuthong, Charyl Chappuis (Javier Patino 46'), Jirawat Makarom, Suchao Nutnum, Adisak Kraisorn (Bruno Herrera 65'), Jesus Berrocal.
Image courtesy of Buriram United FC