Nunez (2), Alexis Mac Allister (pen), Luis Diaz and Dominik Szoboszlai struck for the visitors in the round 1766 first-leg. Conor Bradley also put through his own net.
Klopp later said of Nunez: "He had absolutely more than (an) OK first season but he had to adapt, that's done, and he is settled in the middle of the team.
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"Wonderful guy, wonderful boy. He loves to play for this team together with these boys and has quality coming out of his ears, to be honest.
"It's like strikers are, they score and then they don't score.
"Is he at his absolute peak in general? Not now for us. But can he develop? Yes. Is he a threat all the time? Yes."