Jurgen Klopp was delighted with Liverpool's 4-0 win against Barcelona at Wembley on Saturday, but the German warned his players not to get too carried away with the result.
Liverpool won their International Champions Cup clash against the La Liga champions thanks to strikes from Sadio Mane - his first since joining the club from Southampton for £36m earlier this summer - a Javier Mascherano own goal, Divock Origi and Marko Grujic.
However, Klopp was keen to stress that Saturday's resounding victory over the Catalans would count for nothing when the Premier League season got back underway for his team with a trip to Arsenal, live on Sky Sports 1, a week on Sunday.
"It was a wonderful lesson for us today because we did really well, but when we become a little bit passive, it is a problem for us," Klopp told Sky Sports after the full-time whistle. "That is normal, not only against Barca, but especially against Barca."
"Wonderful goals, great challenges. We wanted to do high pressure, which I think is important against Barca. But of course you cannot do it the whole time and you have to be compact against Barca.
"We have to learn better that when we stay deep, we must be active and it was a little bit of a problem, but there were also some wonderful moments."
The Liverpool boss was also overwhelmed by the huge support his team got from the large proportion of Reds fans among the 89,845 supporters at Wembley.
"I am really happy and emotional about the reaction here in London," he said. "But Liverpool came to London today and it was really nice to have all these people here, 90 per cent on our side, which you do not often get in a match."
As for the match itself, it was not just Liverpool's high pressing game that pleased Klopp, but also some of their passing, especially in the second half as his side scored three times to complete a resounding victory.
"It was not only the high pressing [that pleased me]," he said, "but after winning balls it was the direction of some of our passes and Kevin Stewart's for Divock [Origi's goal].
"We are not at 100 per cent fitness wise, so it is normal too, we had to run a lot, much more than Barca, but we did it and we did it well.
"And scoring goals too - Sadio had a few chances in the last few games, which he did not convert, so it was good for him. [Roberto] Firmino has been the man of preseason for me as from the very first game he has been performing, even if he has not scored. What a worker!"
And while Liverpool did lose makeshift left-back James Milner to a heel injury just before half-time, Klopp did not think it too serious with a trip to the Emirates to come in just over a week's time.
"Defence was good and hopefully Milner is not too serious, it was a bruise, which was painful and he was limping for 35 minutes," Klopp said.
"There were a lot of things I could enjoy, but a lot of things to improve too and at the end, when you lose, you think it is only a test game and when you win you can think it is only a test game. But it is still a good game from our side and that is absolutely OK."
Klopp was keen to guard against complacency, though, especially as, according to him, Barca were only playing at two thirds of their normal capabilities.
"Being good is one thing, but being too satisfied about it is another and we have try and carry on and keep on going, which is very important for us," he said.
"We are pretty sure about our quality, but we have to show it all the time and we also of course need a bit of luck with injuries.
"We had an absolutely OK preseason and yes we beat Barcelona 4-0. But I know they can play better and even then when they play at 60-70 per cent they are pretty good unfortunately, so we have to go 100 per cent, but that is not a problem and that is what we want to do.
"It is a good sign, but not a decisive sign and we would have known about our preseason even if we had lost today, but it is nicer like this to be honest."