Manager Jurgen Klopp said Liverpool struggled to "find their mojo" as two early goals from Milan Pavkov gave Red Star Belgrade a shock victory in their Champions League group-stage encounter.Victory would have taken Liverpool three points clear at the top of Group C but they drop to second following Napoli's draw with Paris Saint-Germain in Italy.
Forward Pavkov headed his side into the lead after 21 minutes and fired a powerful effort into the bottom corner to make it 2-0 shortly afterwards.
"I saw a few games like this already and it is really difficult to find your mojo," Klopp said.
"We made life a bit too easy. I don't say it is already serious if you lose twice but we have to make sure it will not not happen again.
"We had a lot of moments when we could get in control of the game and we didn't do it, we just made the wrong decision."
Red Star dominated the first half and came close through Vujadin Savic and El Fardou Ben Nabouhane before Pavkov's opening goal.
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Klopp's side had more than 80% of the possession and hit the woodwork twice in the second half but could not score as Red Star recorded their 10th clean sheet in their last 15 home games in Europe.
Liverpool host Fulham in the Premier League on Sunday (12:00 GMT), before returning to Champions League action against Paris St-Germain on 28 November (20:00 GMT).