Melbourne Victory suffered their first Asian Champions League defeat under Carlos Salvachua, losing to K League 1 side FC Seoul 1-0.
Seoul snatched a home lead after just eight minutes through Park Chu-Young, while Victory largely held their own but spurned a number of chances on Tuesday night.
Storm Roux's injury saw Ben Carrigan called into Victory's back three, while Jay Barnett made his ACL starting debut in midfield, replacing Anthony Lesiotis.
Seoul struck through their first genuine chance.
Kim Ju-sung powered down the touchline and delivered a cross that skidded through the Victory defence, where Park made no mistake with a lethal left-foot finish.
In the 11th minute, Victory spurned a gilt-edged chance.
Ola Toivonen put through a ball for Adama Traore, who found himself one-on-one with Seoul goalkeeper Yu Sang-hun but failed to connect with his attempted toe-poke, allowing Yu to clear.
Seven minutes later, Toivonen cut between two defenders and unleashed a cracking attempt, forcing a superb save from Yu.
From Migjen Basha's corner, Giancarlo Gallifuoco nodded a header to the back post, where Toivonen put a difficult shot off-target.
Barnett was replaced by Lesiotis through injury on the half-hour mark.
Andrew Nabbout went on a mazy run inside the 18-yard box in the 38th minute but was thwarted, summing up Victory's frustrating opening half.
Seoul vastly improved after the break and nearly doubled their lead a minute into the second half.
Ko Kwang-min's wicked cross found Park, who beat Gallifuoco to the header, but directed it straight at Lawrence Thomas.
Victory's best chance came when Kim Nam-chun's attempt to block Nabbout's scintillating 57th-minute cross saw the defender just inches away from turning the ball into his own net.
In the 78th minute, Brandon Lauton evaded several defenders but was unable to put his curling shot on target.
Seoul's Han Chan-hee had an 84th-minute strike graze the post, while Victory substitute Marco Rojas had a late shot saved.