Seoul scored twice in the last seven minutes to snatch a 3-2 victory from the jaws of defeat away to Kawasaki Frontale in their first leg, while Kosei Shibasaki's injury-time strike gave Sanfrecce a two-goal cushion to carry to Western Sydney Wanderers next week as they won 3-1.
Elsewhere, Salem Al-Dawsari hit the only goal as Al Hilal won at Bunyodkor and Al Sadd's hosting of Foolad ended goalless.
The day’s first two matches kicked off simultaneously in Japan, but by half-time they had not produced a goal between them.
Shortly after the restart, however, the deadlock had been broken in both.
Yoshito Okubo tricked Kim Joo-young down the left and crossed for Yu Kobayashi to head Kawasaki ahead, only for Spain-born Sergio Escudero to equalise following superb wing play from Yun Il-lok.
Just past the hour, Renatinho won and converted a penalty to restore Kawasaki's lead, and with goalkeeper Yohei Nishibe in fine form, the hosts appeared set to earn an advantage to take to the South Korean capital.
However, Kim Chi-woo’s drilled finish after 83 minutes restored parity, before Yun robbed Jeci of possession deep into injury time, accelerated into the Kawasaki box and coolly slotted the ball home under pressure.
Kawasaki will travel to Seoul having scored just one goal in their last six away games in the competition.
Naoki Ishihara's brace, including a delightful chip, sent Sanfrecce into a 2-0 lead against Australian's Western Sydney Wanderers, but Tomi Juric earned and dispatched a penalty to halve the deficit.
With virtually the last action of the game, however, Kosei Shibasaki crossed a free-kick into the box, which deceived Ante Covic and his defenders to complete a 3-1 victory for Sanfrecce.
Bundyodkor monopolised possession at home and hit the woodwork twice, but Al Hilal returned to Saudi Arabia with a victory thanks to Al-Dawsari reacting first to a loose ball shortly before half-time.
Finally, the reflexes of Soosha Makani were responsible for earning Foolad a 0-0 draw in Doha.
Al Sadd will not be too disappointed, however, given that Brazilian striker Luciano Pereira spurned a great chance to give the Iranians a crucial away goal.
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