ACL loss wake-up call for Sydney FC: Arnie

They admit Suwon Bluewings offered few on-field options, and Sydney FC must figure some out quickly if dreams of conquering Asia are not to be short-lived.

Wednesday night's 2-0 opening Asian Champions League loss dealt the domestically dominant Sky Blues what coach Graham Arnold branded a harsh "wake-up call" about the continent's tactical nous.

Every possible move was keenly anticipated by the South Korean outfit who, despite still being in pre-season and enduring a near 40-degree change in climate, sit atop the group.

The well-structured Suwon had clearly done their homework, switching to three at the back to stifle the creative outlets that have yielded Sydney 50 A-League goals from 20 games this season.

Just as surprising was that the defeat was suffered at home, where Arnold's side had not ceded more than a point in the 22 months prior.

Now last though with five games still to play, they must travel to China, where they have everything to do against Shanghai Shenhua to avoid slipping too far off the pace for a knockout-stage berth.

As Arnold rightly pointed out, Sydney lost their first match in 2016 and still went on to top their group.

But that was away in Japan, and not a single home game was sacrificed that campaign.

Arnold admitted his team were off colour and cited futile attempts to "walk the ball in", or eschew simplicity and "give the killer pass".

"It's a wake-up call, not only for the players but for the staff and everyone," Arnold said.

"You come up against a strong opposition and big, powerful, strong boys with pace.

"We conceded two sloppy goals, and our defence is normally very strong.

"But they were hard to break down. We had a couple of half-chances but you need better chances than that at this level."

Arnold labelled Suwon as Sydney's toughest opposition of their 18-month A-League supremacy.

Midfielder Brandon O'Neill agreed but stressed there was not a gap in class, rather a need to adjust to Asia's style.

"In the A-League teams press more, they leave a little bit more space, and Suwon made it difficult for us," said O'Neill, who conceded an unlucky late penalty.

"It's a real eye-opener, Asian football is very good ... the speed and the quality of play.

"You think you have an option, you think you have a pass, then all of a sudden in a split second it's gone.

"You need to readjust your thinking and play a better ball."

Shanghai drew 1-1 with Kashima Antlers in Wednesday's other Group H tie.