It was the wake-up call Graham Arnold said Sydney FC needed, with an opening AFC Champions League loss leaving the A-League champions everything to do in China next week.
The Sky Blues were outscored and ultimately outplayed in Wednesday night's opening 2-0 loss to Suwon Bluewings.
Last in Group H -- albeit with only one of six matches played -- they must re-group and aim for three points away to Shanghai Shenhua next week to stay on course for the round of 16.
With Suwon still in their K-League preseason and missing a couple of key players including Matt Jurman, the defeat -- Sydney's first loss at Allianz Stadium in 22 months -- represented a big opportunity missed.
While far from content with the performance, Arnold felt the South Korean qualifiers were Sydney's toughest opposition in the good part of two years.
"Probably, but that's Champions League," Arnold said. "That's what happens if you're not at your best and you play against a good opposition.
"It's a wake-up call, not only for the players but for the staff and everyone.
"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."
The well-structured Suwon had clearly done their homework on Sydney and, along with switching to three at the back, stifled Adrian Mierzejewski and kept Michael Zullo relatively quiet.
"Then you're looking for other players to fill in or step up," Arnold said.
"Our last ball wasn't great. If there's one negative it's that we weren't brave to shoot from the second line, we were trying to walk the ball in or give the killer pass when a shot from 20 metres could have changed the game exactly like their first goal.
"There's still five games to go. Last campaign we lost the first game and came home strong and ended up winning the group."
Shanghai drew 1-1 with Kashima Antlers in Wednesday's other Group H tie.