Jurgen Klopp could not contain his slight frustration as Liverpool shipped two late goals in their enthralling 5-2 victory over Roma at Anfield.
A magnificent double from Mohamed Salah, Sadio Mane's calm finish and Roberto Firmino's brace had put the Reds in dreamland as they looked to all but seal a place in the final.
But Roma rallied and struck twice in the final ten minutes through Edin Dzeko and Diego Perotti to maintain a slim chance of progression.
Klopp was delighted with one of the best attacking displays of his tenure but bemoaned the "little mistake" which handed the visitors a route back into the contest.
"Long-term perfect performance for pretty much 80 minutes or so," he said. "We made defensively one mistake. The penalty is not a penalty but that is the situation and now it is 5-2.
"Of course we would have been more happy with 5-0 or 5-1 but 5-2 is a fantastic result. We go there and try again.
"We had all these runs behind, it changed the game completely and they couldn't cope with that. We scored these goals and could have scored more.
"That is all positive, at this moment it doesn't feel all positive because they scored these two goals but tomorrow I will see the really good part of the game.
"It is absolutely better than I thought before the game but at the moment of course a little mistake."
Ox injury tarnishes memorable night
The other dampener came in the form of a first-half injury to Alex Oxlade-Chamberlain, who looked in serious pain after a clash with Aleksandar Kolarov and was stretchered off.
Asked about the severity of the injury, Klopp was not optimistic and fears the Englishman's season may be over.
"Oxlade-Chamberlain is probably a really bad injury," the German admitted. "That is bad news for us. The squad doesn't get bigger at the moment so we need to be creative in the next few games."