By Gabriel TanFollow @@gabetan13
Following a goalless first half at the Seoul World Cup Stadium that saw Carmelo Gonzalez miss a penalty for the visitors, Seoul took the lead in the 54th minute when Jung Seung-yong scored from close range, but they were pegged back two minutes later when Ekkachai Sumrei tapped home a Kai Hirano layoff.
16 minutes from time, the K-League giants edged ahead again when Kim Hyun-sung sent a glancing header into the bottom corner, but this time it took Buriram just a minute to respond; Theerathon Bunmathan curling home a freekick from the right wing.
With neither side able to find a winner in the closing stages, both had to settle for a share of the spoils, which proved enough for Buriram to seal a top-two finish and progress to the next stage thanks to Jiangsu Sainty's 2-1 win over Vegalta Sendai in the group's other encounter.
Yet, it could have been much easier had the Thunder Castle been able take advantage of the fact Seoul manager Choi Yong-soo named a weakened starting XI given his side had already wrapped up top spot last week.
But although the visitors did get off to a bright start, it was Seoul who created the better of the chances and Ko Kwang-min was wasteful in the 17th minute when was picked out unmarked inside the area by Kim's well-weighted cross but sent a free header over.
Two minutes later, it was Kim's turn to miss a good opportunity when he could only fire wide after a loose ball had fell into his path on the edge of the area.
Six minutes after the half-hour mark, Buriram were fortunate not to concede a penalty when Jung found space inside the area and fired in a shot that smashed off Adisak Kraisorn's hand, only for referee Faghani Alireza to wave play on.
And five minutes later, the hosts had every right to feel aggrieved when the Iranian official awarded the Thunder Castle a penalty after Han Tae-you was adjuged to have dragged Kai Hirano back inside the box.
With seven goals to his name so far in the Thai Premier League, many would have expected a 12-yard shot to pose no problem to Carmelo, but his effort lacked any real conviction and Yu Sang-hun was able to tip it wide comfortably.
A minute before the break, Yu did however had a more difficult save to make when he raced off his line well to deny Adisak in a one-on-one chance, after the winger had broken free inside the area.
Nine minutes after the break, Buriram were made to pay for their profligate ways when the hosts opened the scoring; Ko breaking free down the right and playing in a perfect cross for Jung to sweep home from inside the six-yard box.
But before Seoul had fully completed their celebrations, the visitors pulled level in the 56th minute when Carmelo's shot from the edge of the box, was deflected into the path of Hirano, who instantly laid the ball to Ekkachai. The 24-year-old coolly slotted the ball past Yu and although the opposition players furiously appealed for offside, replays showed the officials were right to let the goal stand.
Nonetheless, a draw would still not be able to guarantee Buriram progress and aware that Jiangsu were currently holding Sendai to a 1-1 draw, the Thais continued to push forward in search of a winner but in the 74th minute, it was the hosts who went ahead once more.
Just nine minutes after coming on, substitute Mauricio Molina floated a dangerous 35-yard freekick into the box that landed straight onto the head of Kim, who got just enough of a touch on the ball to divert it past Sivaruck Tedsungnoen and into the bottom corner.
However, just as they did with their first equaliser, it took the visitors less than 60 seconds to pull level once more; Theerathon lining up a freekick on the right and sending in a delightful swerving effort that bounced right in front of goal before skipping past a confounded Yu.
After that, both sides did show good initiative in the search for a winner but neither were able to find a decisive third and had to settle for a draw, although Sendai's defeat meant it was enough to send Buriram through to the last 16.
In doing so, Attaphol Puspakom's men also made history by becoming only the second side from Thailand to make it out of the group stage, following in the footsteps of BEC Tero Sasana, who reached the inaugural Champions League final back in 2003.
FC Seoul: Yu Sang-hun, Choi Hyo-jin (Adilson 46'), Kim Nam-chun, Han Tae-you, Kim Chi-woo, Ko Kwang-min, Lee Sang-hyeob (Park Hee-seong 88'), Choi Hyun-tae, Choi Tae-uk, Jung Seung-yong (Mauricio Molina 65'), Kim Hyun-sung.
Buriram United: Sivaruck Tedsungnoen, Suchao Nutnum, Tanasak Srisai, Prathum Chuthong, Theerathon Bunmathan, Surat Sukha, Jirawat Makarom, Adisak Kraisorn (Attapong Nooprom 89'), Kai Hirano, Ekkachai Sumrei (Suriya Domtaisong 81'), Carmelo Gonzalez.