Seoul set up an all-Korean AFC Champions League semi-final after a 4-2 aggregate win over Shandong Luneng.
A late goal from Yun Ju-tae sealed a 1-1 second-leg draw for the visitors at Jinan Olympic Sports Center on Wednesday and booked their safe passage into the last four, where they will face Jeonbuk.
Shandong, who were beaten 3-1 in the first leg, went on the attack from the outset but struggled to find a breakthrough, with Graziano Pelle twice coming close with headed efforts.
Walter Montillo grabbed a lifeline for the Chinese Super League side with a fine header on the hour mark, but after holding off some sustained pressure, Seoul made their progress safe seven minutes from time as Yun steered a fine finish past Wang Dalei following Dejan Damjanovic's clever lay-off.
In the last of the four quarter-finals, El Jaish battled to a 1-0 win to earn a semi-final spot in controversial fashion over Al Nasr.
The UAE side won 3-0 in the first leg, only to see that result overturned by the Asian Football Confederation after it was deemed that Wanderley - who scored twice in that game - was ineligible to play.
El Jaish were consequently awarded a 3-0 victory by the AFC, and they made their place in the last four all-but secure after just nine minutes of Wednesday's meeting at Al Maktoum Stadium, when Romarinho smashed in Seydou Keita's delivery.
Al Nasr pushed hard for a lifeline, taking 20 shots across the 90 minutes, but Khalifa N'Diaye was in strong form in the visiting goal to help his side preserve their 4-0 aggregate lead and set up a showdown with Al Ain in the next round.