The Magpies need to beat the Portuguese club by two clear goals if they want to progress to the Europa League semi-finals and only Barcelona have achieved that feat over Jorge Jesus' men this campaign.
"There's only one team which has beaten them by two clear goals, and that's Barcelona, so that's the size of the task, so we are under no illusions there," said Pardew of Benfica who have not lost in their last 31 outings.
"This is a Champions League team, really, and if it weren't for Celtic's fantastic performance in the group, they could have been competing in the Champions League.
"That's the quality we are up against. I don't think there are going to be many better sides that have played here than Benfica.
"They have a slightly different style to a Premier League team. They have some fantastic technical players - Gaitan, Rodrigo, Cardozo and Lima.
"They have a real, real threat on the counter-attack, and the game could get away from us - it could easily get away from us - so we have got to be very much on our guard that we approach it in the right manner, give ourselves a chance and try to get us to the end of the game in a position where we can get it back.
"I would still feel confident two goals down with 10 minutes to go, the way that we are and the potential we have in the group, and the way I can affect it off the bench."