Tony Popovic declared Western Sydney Wanderers' 4-0 capitulation at home Urawa Red Diamonds on Tuesday night was a sharp reminder of the AFC Champions League's (ACL) quality.
On a disappointing night for the 2014 ACL champions, the Wanderers held out till half-time before the J.League powerhouse smashed four past Vedran Janjetovic to register a convincing win in their Group F opener.
Despite Popovic's claims to the contrary, Western Sydney were hardly in the contest at Campbelltown Stadium as they failed to register a shot on target throughout the 90 minutes.
"You realise very quickly the level of this competition, and you get punished for your mistakes," the Wanderers' coach told Fox Sports.
"It makes you realise what can happen here [in the ACL]."
Popovic selected a relatively inexperienced Wanderers side against the 2016 J.League runners-up with six changes to the starting XI that won the Sydney derby on Saturday night.
Aritz Borda and Brendan Hamill replaced Rob Cornthwaite and Jonathan Aspropotamitis in central defence, Dimas returned to defensive midfield ahead of Terry Antonis, while Popovic selected Jumpei Kusukami, Steve Lustica and Abraham Majok as his front three.
Brendon Santalab, Mitch Nichols and Jaushua Sotirio made way.
Beanpole teenage striker Majok made his senior debut against the Reds.
"It's something he'll [Majok] never forget, playing in the Champions League. He held his own and I'm sure he'll learn from it," Popovic said.
Urawa, who will first start their domestic season this weekend, were far more dangerous throughout the game.
The visitors finished with 10 shots to three, 56.6 per cent possession, 527 passes to 401 and 17 tackles to nine.
After a scoreless first half, two goals in three minutes saw Mihailo Petrovic's men take control, with Shinzo Koroki and Tadanari Lee converting.
Central defender Tomoaki Makino made it 3-0 from a corner in the 68th minute, while substitute Rafael Silva wrapped up Urawa's victory with four minutes left, notching his first goal for the Japanese club.
"At 0-0 we were in the game but just as we were having a few good moments and getting on top, we got punished," Popovic argued.
"And that's what you get at this level and they are a very good side."
The Wanderers' next game is away to Perth Glory in the A-League, while next week in the ACL they will travel to Shanghai SIPG, who started Group F with a 1-0 win at FC Seoul.