And with that, a 2-0 win that leaves Liverpool in a really tricky spot.
"I saw a few games like this already and it is really hard to find your mojo", Klopp said.
I don't say it is already serious if you lose twice but we have to make sure it will not not happen again.
"In the end you have to score goals in a game and if you think about how often we were in the box and around, that's what you have to do in a game but you have to make the last decision in the right way and we didn't".
A first-half brace from Milan Pavkov earned Red Star all three points.
"We had the first big chance with Daniel, a very big one".
However, they are a different proposition at home and after holding Napoli to a 0-0 draw in their group opener, they kept Liverpool at bay after the break.
Klopp said: "Pretty much the first time all the midfield players apart from Ox are available".
"At half-time, we tried to change a few things and did that".
It was no more than Red Star deserved after the opening 20 minutes, with center back Vujadin Savic firing over before El Fardou Ben Nabouhane forced Liverpool keeper Alisson Becker to palm his low drive from 25 meters around the post.More news: Yankees MLB trade rumors: Giancarlo Stanton to make room for Bryce Harper?
"There's only been two games, now Red Star and Napoli (where we haven't been)".
Klopp needs to find a way to utilise his new resources and rediscover Liverpool's mojo quickly to avoid an embarrassing early European exit.
Crvena Zvezda fans had a choice greeting for Liverpool when the two sides met in Belgrade for their UEFA Champions League Group C clash on Tuesday - with a pre-match choregraphed rendition of "F*ck you Liverpool".
Robertson added, "Maybe it's not been as good to look at but we've been effective at it".
"We have 27 points".
"The atmosphere noise wise was not a problem for us".
"They were on their bikes and we had to deal with the situation".
"(It's going to be) very tough. We all have to deal with it.
"We were not surprised by Red Star's tactics".
Liverpool are unbeaten in the Premier League, and sit top of the standings in Group C, hence they sought to further strengthen their qualification position by getting a victory in Belgrade, but their hosts had other ideas, as they outplayed their more illustrious visitors to deliver a result which nobody foresaw. The Reds failed to land a shot on target in their other away game in the competition this season vs Napoli.