That doesn't mean Victory won't produce something to surprise him, but he said he was ready for that too - as ready as you can be, anyway.
"You've got to be ready for anything," Janjetovic said.
"On the day, you're never going to know for sure what's going through an opposition player's mind, you're never going to know someone inside out, but you can prepare well enough to get a good idea of what a certain player may do in certain situations.
"They will try to surprise you as well, which is why you can never think you can sit back on your heels in a game like this. If you relax, even for a second, you're asking for trouble.
"They're going to come at you and they're going to want everything. Whatever you give them, they're going to take, so we'll try not to give anything away. We'll try to keep it tight and do everything we can to be the best."
As unfair as it may be, the focus is inevitably on the goalkeeper when a team concedes a goal, but the fact is the opposition has to get past the outfield players first, before it can think about scoring.
Asked how Sydney FC prepares to try to cope with a Victory attack that includes Gui Finkler, Kosta Barbarouses, Fahid Ben Khalfallah and Besart Berisha in the front third, with Archie Thompson waiting on the bench, Janjetovic revealed the elements of a very thorough process.
"The playing group sits down with the coaching staff and we break down the opposition," he said. "This is their defensive structure, this is their middle and this is their attack.
"If we try to look at it in one big picture it's too much to take in, because they come from everywhere, so we look at it in three divisions.
"Everyone is free to give their opinion. It's the same when we discuss our attack. This is how they defend, so what's the best way to get around that with our attack.
"After that, we get the defenders in together and it is explained to them what their job roles will be and who they're marking, and it's the same with the midfielders and attackers.
"At the end, we bring everyone in and show a video of about five to 10 minutes on the opposition's style of play. Once everyone understands their job roles and how the opposition operates, it's much easier to watch that video and know what you've got to do."
Janjetovic said he did his own video work on opposition attackers as well.
"I sit down with the goalkeeping coach and we'll look at how they operate," he said.
"If a certain player has got the ball out wide, what are his options normally. Is he the type of player to whip a ball in or will he take someone on and try to cut it back.
"We'll start by defending from the front, so our strikers will be the first point and if it does get to the middle or the back end then hopefully we've got enough men there and we'll react well enough to break it all down.
"We've got to look at everything that may happen. We certainly do our homework in that department.
"Victory played a game against Central Coast recently and Finkler scored two goals with shots they wouldn't have been expecting. They were great shots, too. We've got to be ready for them to try something that is unusual.
"The Victory attackers have each got something different and they're all lethal in their own way. From Finkler to the outside guys to the front man, there are so many combinations they can come up with and sometimes you look at it and it's scary.
"That's why you've got to be as ready as you can be.
"They've got depth everywhere, from the back coming forward and especially in that front third. They're a big force, they've been a big force all season. We've prepared as well as we can and we'll leave nothing out there on the field."
It's a lot to cover, but Janjetovic believes he is ready for the ultimate challenge.
Asked if he felt he knew Victory's game as well as he possibly can, going into a winner-take-all match, he replied: "I think I do, yeah. I think everyone across the board in our team will tell you that they do, because we do a lot of work on them.
"We played them three times during the regular season, so we know what they're about, what they can bring to the table and what they're capable of doing on a good day.
"Victory finished on top of the table because they deserved to be there. They're the form team of the competition. We have to come ready for a huge battle on Sunday."
