Klopp, whose side will defend a 2-0 lead from last week's first leg at the Estadio do Dragao on Wednesday, added that last year's match was "really strange".
Liverpool met Porto in the round of 16 last season, drawing the return 0-0 at Anfield after their runaway first-leg win.
"The first goal was really good play but Sadio (Mane) had harder shots that weren’t in. The second goal was great play and (Mohamed) Salah finished it off from the post. And then three counter-attacking goals that were really good," he said.
"I didn’t like the last game. It was really strange... It was really open until we were 2-0 up but you don't remember things like that. But my players aren’t silly, they don’t misunderstand this."
"Porto are a really, really good football team. We have to play at our limit 100 percent," he said, adding that the Portuguese side had won all four Champions League home games this season.
Klopp went on to warn his team about the atmosphere they would face.
"I was here for a derby years and years ago and...yeah...that was loud," he said. "They know how to influence a game and an opponent and we have to be ready for this atmosphere."
Centre back Joe Gomez, who has been sidelined since December after having surgery for a leg fracture, could make his return, Klopp added.
"Joe is getting better and better and better," he said. "Can he play 90 minutes in the Champions League? I am not sure, but no need to think about it. Can he come on and do a great job? Yes, no doubt..."
(Writing by Brian Homewood; Editing by Toby Davis)
