Leading Napoli 1-0 through Mohamed Salah's 12th goal of the season, the Brazil international produced a point-blank block from substitute Arkadiusz Milik to ensure his side got the exact scoreline they needed to progress to the knockout stage.
He said: "The goal Mo scored - what a goal, unbelievable - but the save Ali made I have no words for that. That was the lifesaver tonight.
"It was not only one save. He had a lot of things to do tonight. How cool and calm he was with the ball helps us a lot in our build-up situations. When he comes out for crosses he is outstanding.
"And, yes, that save was just incredible, but if we don't defend the whole pitch like we defended, Ali cannot make 20 saves like the last one.
"He did it - incredible, unbelievable. I never saw something similar."
Liverpool went into the game having to judge a finely-balanced conundrum of winning 1-0 or beating the visitors by two clear goals. In truth they could have scored four or five and Klopp was impressed with how they played.
He admitted: "I am still full of adrenaline. This game was just amazing, outstanding, unbelievable, the boys left their whole heart on the pitch. Our offensive defending and pressing was some of the best I ever saw."