Liverpool appeared to have it in control as they battle Sevilla and got an early lead from Sadio Mane after 30 minutes.
But the Reds defensive frailties showed again as Sevilla was able to create an added-time equaliser.
“We stopped playing football in the second half,” Jurgen Klopp said.
“We have one real weapon — playing football — and we didn’t do that in the second half before we conceded the second goal.
“It was absolutely OK that we were confident after that first half. It’s obvious what we did — the real problem is we stopped playing football. Our main mistake was that for 15 minutes we didn’t play football, we were passive, we were a little bit too deep. They fought back and well done to them.
“It feel like we lost but we didn’t lose. There is a game to go and it’s still in our hands but at the moment it feels really bad.”
Liverpool captain Jordan Henderson also said that he is unsure when the collapsed happened.
“I am not sure (how the collapse happened). The first half was very good, disciplined, score good goals,” Henderson said.
“The second half was very bad, we did not start well at all. We gave a corner away and struggled from then on.
“We stopped playing football and did not get the ball to the front three to cause them problems. it does not feel good.
“The message at half-time was to keep going and they were going to give it a right go, they had nothing to lose and we could not cope with it. At least it is still in our hands to top the group.”