Lee Cattermole says Sunderland will be backing themselves to get the better of Pompey over two legs, despite not beating them so far this season.
The two sides have met three times in the current campaign, Portsmouth 3-1 winners at Fratton Park in December, a game that was level at the break before Glenn Loovens saw red.
They then edged out Sunderland in the Checkatrade Trophy final at Wembley on penalties, before a 1-1 draw at the Stadium of Light last month.
The Black Cats were much the better of the two sides in that game and Cattermole believes there is nothing for his side to fear.
"The first game, with Luke's goal, I believe we should have gone on from there but we let in another, not the best of goal in," he said.
"Portsmouth are an experienced side, an experienced manager, they know the league well and you can see when they came up here, they were more than happy to get away with a point.
"Later on in the game, I felt they were more than happy to slow it down. We've got to fancy ourselves.
"From what we've seen, we need to be really good in both boxes, clinical in one and really tough in the other, because they're a big, physical side, they got on top of us in the second half at Wembley and made it difficult for us, but we're excited about this game," he added.
"The intensity in training has flown up, because I'm pretty sure everyone is looking at Saturday and wanting to be in that team. I think it will bring out the best in us. We can't go out and try and win it in ten minutes, there's two games in the tie, we have to play with our heads."
Cattermole believes being more clinical will be key to Sunderland finally getting the better of Kenny Jackett's side.
"We need to take our chances a bit better," he said.
"We've had some good chances around the edge of the box, maybe we need to keep the ball high up the pitch for longer periods, that's maybe something. It will be interesting to see how both teams approach it, it's an exciting game and as a group we fancy ourselves.
“Just winning games has been something we’ve had to learn this season. That’s probably let us down as well, too many draws. We had a lot last year as well.
“That’s something we’re aware of and I think if we can keep a clean sheet in one of the two legs, I think it will stand us in good stead because that’s when we’re at our best, when we’re keeping clean sheets," he added.
“The second goal will be important for us [if we can get ahead]. I don’t think we’ve got the second goal enough. We’ve had good chances.
“Just thinking about the game, I can imagine the first one being cat and mouse.
“Games are won and lost in both boxes.
“I think the home league game was as solid as we’d played in 90 minutes, we played really well on the day but their goalkeeper was excellent.”