Gamba Osaka are in pole position to qualify for the AFC Champions League quarter-finals following a 3-1 win at Seoul in the last-16 first leg on Wednesday.
Forward Takashi Usami scored a second-half double, while Koki Yonekura was also on target for the J-League side, with Yun Ju-tae pulling one back late on for the hosts.
By contrast, Seoul's K-League rivals Seongnam will take a slim advantage into their second leg after a 2-1 victory over 10-man Guangzhou Evergrande.
Jorginho put Seongnam ahead 23 minutes in before a 30-yard finish from Huang Bowen levelled matters for Guangzhou.
But the visitors were reduced to 10 men after 65 minutes as defender Li Xuepeng was sent off for a rash challenge on Ricardo Bueno.
Seongnam did not find the winning goal until the 96th minute, though, as captain Kim Do-heon netted from the penalty spot.
A 34th-minute Gholamreza Rezaei strike gave Naft Tehran a 1-0 win over Al Ahli of Saudi Arabia, whose namesakes from the United Arab Emirates drew 0-0 with domestic rivals Al Ain.
