Coaching staff and players from both sides fought on the pitch at the Suwon World Cup Stadium following Al Sadd striker Mamadou Niang's controversial second goal in the 81st minute.
In some appalling scenes, players could be seen kicking at each other, while others ran away from the fighting as a number of scraps took place across the field.
The Koreans were unhappy that Al Sadd had quickly restarted play and set Niang through unopposed to round goalkeeper Jung Sung-ryong and score.
Before the controversial goal, Suwon had allowed the ball to go out of play after one of their players went down with a head injury in the Al Sadd area.
The game then restarted with Al Sadd forward Kader Keita passing to Niang as Suwon players, slowly walking back to their positions thinking their team mate was still being treated, were unaware the referee had allowed the game to continue.
"Clearly, Yeom Ki-hoon had put the ball out and I think it is the situation when our players should get it back," Suwon coach Yoon Sung-hyo told reporters.
"The opposition scored an ungentlemanly goal but there's nothing we can do about it."
Suwon players and coaching staff remonstrated with the referee and then their Al Sadd opponents as fighting broke out in dreadful scenes that will surely lead to heavy sanctions by the Asian Football Confederation (AFC).
Fans vented their frustration by throwing objects on to the field during the scuffles with one supporter running on to the pitch.
After things had calmed down, Singaporean referee Malik Abdul Bashir showed a red card to Suwon's Stevica Ristic and Al Sadd's Keita but he could have easily awarded more such was the scale of the fighting.
Al Sadd coach Jorge Fossati said the pressure of defending for long periods had led to the mix up in not returning the ball to Suwon.
"There were two players injured and my players were feeling a little pressure emotionally as Suwon were continually attacking," the Uruguayan explained.
"Of course, I don't want to defend the second goal but I think that Niang lost his head and made the decision to attack by himself."
Niang was sent off shortly after collecting a second yellow card for kicking the ball away as the final minutes were played out amid a simmering tension and a number of rash tackles by both teams, who meet in the second leg in Doha next Wednesday.
Champions League controversies continue to follow Al Sadd who could consider themselves fortunate to be in the last four.
The big-spending Qatari's lost both matches in their quarter-final only to be awarded a 3-0 first leg win by the AFC after Iranian opponents Sepahan were deemed to have fielded an ineligible player.
The early action in Korea on Wednesday had been pla
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