Quickfire goals from Marko Pjaca and Dani Alves helped the Serie A champions to a 2-0 win at the Estadio Dragao three weeks ago, with Porto likely needing to score at least three goals to stand a chance of reaching the last eight.
Barca's turnaround against PSG last week - from 4-0 down to win 6-5 on aggregate - may give Porto's travelling fans hope, but Nuno says the comparison will not help him plan a victory against Massimiliano Allegri's side.
"We are behind in the tie but there are no parallels to be drawn with what Barcelona achieved last week," he told a news conference. "We must consider this as a completely different, one-off game.
"Beginning in the play-offs in August, we've come a long way to get to this point and the team can be proud of what they have achieved so far.
"We have a clear idea of how we want to approach the game; we want to attack, be effective at both ends of the field and give our creative players license to influence the proceedings as best they can.
"We have come here in good form, high spirits and we have the belief to get the result we want. Everyone knows how strong Juventus are on home soil. Their records speak for themselves but eventually someone will beat them here and it could be us that does it."
Porto have won nine Primeira Liga games in a row, a run only blotted by their first-leg loss to Juve, and midfielder Yacine Brahimi echoed his coach's positive sentiments.
"We are preparing for a tough game against top opposition but we believe we have it takes to reach the next round," the Algeria playmaker said.
"The way we have trained and performed as a group in recent weeks has demonstrated that and we are confident that we will produce a worthy performance."