The Magpies must overcome a 3-1 deficit if they are to reach the semi-finals of the competition.
Newcastle were architects of their own downfall in the first leg, with three defensive errors resulting in three goals for the Portuguese League leaders.
Goalkeeper Krul admits the Eagles are the best side they have faced in this season's Europa League but remains confident they can progress to the last four.
He said: "The fans have sold out the stadium because they see it as a massive opportunity for us and we have to see it as a massive opportunity.
"It's a quarter-final of the Europa League, you can't just see it as a friendly game. The games are coming thick and fast. It's Thursday night first and Sunday's (game against Sunderland) another story.
"It's been a long time without a trophy, we know that. Don't get me wrong. Benfica are a tough team.
"It is a different game because they are a top, top squad. It could be a special occasion on Thursday night."
Newcastle are unbeaten at home since January and Krul says there is a positive mood in the squad after Papiss Cisse hit an injury-time winner against Fulham last weekend.
"It lifted everybody," admitted Krul. "Very few grounds have an atmosphere like that.
"It is an amazing time at St James' when you see everybody celebrating like that."