Phan Van Tai Em's equaliser on the stroke of half-time had cancelled out Mota's opener for the visitors but Choi, who scored the only goal in the 1-0 win against Adelaide United two weeks ago, emerged as Seongnam's hero again to send the battle for top spot in Group G to the final match.

With group leaders Shandong Luneng held to a 2-2 draw by Adelaide United, Seongnam host the Chinese champions on May 23 needing to win by a two-goal margin to progress to the last eight.

Luckless Dong Tam, who went down to an injury time goal against Shandong in their last match, stay in last place after suffering their fifth straight loss in Group G.

The heavy rain before the match created difficult conditions at Long An Stadium but the Koreans managed to take the lead after 17 minutes when Brazilian forward Mota launched a long-range effort that caught Dong Tam goalkeeper Santos out of position for his fourth goal of the competition.

Dong Tam coach Henrique Calisto was looking to rest prolific Brazilian striker Antonio for the upcoming Vietnam league matches but the Portuguese coach brought him on in the 27th minute to replace midfielder Phan Thanh Giang and link up on with Congolese forward Kabanga Tshamala.

Antonio's introduction sparked the Dong Tam attack to life and they were unlucky not to level the score in the 31st minute when Tshamala dispossessed Park Jin-sub and fired the ball against the frame of the goal.

Two minutes later, Seongnam captain Kim Sang-sik carelessly lost the ball but Luu Minh Tri's shot was punched out by Seongnam goalkeeper Kim Yong-dae.

The home side's pressure would eventually pay off though in the final minute of the half when playmaker Phan Van Tai Em drew the sides level, crashing home a volley for his first goal of the competition.

Both teams had their chances in the second half as Nguyen Viet Thang and Van Tai Em hit the Seongnam woodwork while Kim Do-heon and Choi Song-kuk tested Santos with long-range efforts.

Kim Dong-hun was a constant threat for Seongnam, as he forced a pair of fine reaction saves out of Santos and hit the post with a 77th-minute header that had the Brazilian goalkeeper beaten.

Seongnam's pressure would finally be rewarded in the 83rd minute when Park Jin-sub exchanged passes with Kim Dong-hun before crossing for Choi Sung-kuk to chest the ball into the Dong Tam net.

Antonio missed with a close-range header in the dying minutes as Dong Tam failed to pick up their first ever point in the AFC Champions League.