Adelaide United's Asian Champions League campaign was effectively snuffed out in a 1-0 away loss to Korean champions Seongnam Chunma.

A superlative 29th minute strike from Choi Sung-kuk was enough to sink United, who are now three points adrift of Seongnam and five back of Chinese group leader Shandong Leuneng.

United will be officially knocked out if Shandong defeat group minnows Dong Tam Long An in Wednesday night's late match in Vietnam to stretch that lead to eight with two matches remaining.

Shandong's five-point break on the rest of the group, meant that Adelaide and Seongnam knew a repeat of last week's see-sawing 2-2 draw at Hindmarsh Stadium would effectively eliminate both sides from the tournament, as only the top team from each group will progress to the next phase.

Team selections reflected the attacking intent of each side, United slipping Bruce Djite and Nathan Burns straight back into the team after Olyroos duty, while Seongnam named attacking options Kim Dong-hun and Choi Sung-kuk to support elusive Brazilian striker Mota.

It was Choi who was to put the vital space between the teams just inside half an hour, beating Reds goalkeeper Robert Bajic with an audacious chip at Seongnam Tancheon Sports Complex.

Adelaide defender Richie Alagich was caught in possession by Choi, then watched helplessly as the striker's instinctive effort sailed over Bajic and into the back of the net.

United worked hard in the second half, bringing on wide men Matthew Kemp and Lucas Pantelis in search of a telling cross, but despite a distinct possession advantage, they could find no reply to Choi's earlier effort.

Reds interim coach Aurelio Vidmar said Choi's goal was of high class but was again due to an unnecessary loss of the ball by his players - a recurring theme of the tournament.

"It was a great goal, but it was as a result of a mistake by us, losing possession at the defensive end of midfield," he said.

"We pushed as much as we could after that but you just cannot afford to give up the ball repeatedly against these sides because they will hang on to it and make you pay."

Knowing his side is now out of contention for the next round, Vidmar looked ruefully back at the draw of two weeks ago, also against Seongnam, which had seemed so likely to finish an Adelaide win when the home side led 2-0 in the second half.

"That was probably the turning point for us in the whole competition," he said.

"Coming over here we could see they were coming under a lot of pressure from the media and the public in Korea, and to have flown over after a win instead of a draw we could have really pushed them."

United return home to Adelaide still not knowing who will be the next permanent coach of the club, though Vidmar remains favoured to be appointed on a fulltime basis.

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