While Sydney are out of the finals reckoning and AFC Champions League to consider, the match is now a huge one for Perth in the wake of the 2-0 loss by faltering Melbourne City to Adelaide United at AAMI Park on Friday night.
Glory will go to at least fourth and get a home game in the first week of the finals series if they beat Sydney.
They could even rise to third with a win - if third-placed Western Sydney Wanderers don't do any better than a draw against Wellington Phoenix at Westpac Stadium in the earlier Sunday game.
A draw against Sydney would leave Perth in fifth place.
While Glory have everything to play for, Janjetovic said the fact Sydney could at least have an effect on the positioning for the finals gave the Sky Blues added motivation.
"Perth are going to come at us hard, they want to get a good result," Janjetovic said. "The only thing we can do is put a spanner in the works for them and make them have to work even harder.
"If we stop them from winning it hurts their chances of finishing a bit higher up the ladder, so while they've got everything to play for we've got plenty of motivation as well.
"We can go out there and enjoy our football and try to give ourselves and our fans a good note to finish the season on. We've got nothing to lose, so it's going to be one of those games, I guess.
"We're not just going to hand them three points just because it's the last game of the season and we can't make the finals. There aren't going to be any giveaways, so expect our boys to come out firing - especially after our good ACL result during the week."
Janjetovic said the Sydney players were all still competing for places in the team for the remaining two ACL group-stage games, which was further motivation not to slacken off or put in a poor performance.
"We're using this game against Perth to push for selections in the ACL and to be ready and fit," Jenjetovic said.
"We've got 10 days between the Perth game and our next ACL game, so we can go hard against Perth and then freshen up before we get ready for the ACL game."
The game against Perth will be the 100th for Janjetovic in the A-League - all with Sydney. He has played his last 83 games consecutively in a great show of durability.
"I've played the last three seasons straight," Janjetovic said. "I think that playing every week and not missing a game for a long time is just about taking care of yourself.
"I do all the work with the team and when I go home I put in a bit extra on recovery and just maintaining the body, through swimming and extra stretching, that sort of thing.
"Doing yoga with the team is another thing. I'm not that great at it, but it definitely helps.
"Playing in the ACL on top of the league has been a test for all of us. There has been a lot of travelling and backing up quickly to play, so it's something new for me and a lot of the other players here.
"But we'll have a good rest after this game, so there's no reason we can't go 100 per cent against Perth. Expect the boys to come out and prove a point to the coach, because everyone wants to get selected for the next ACL game."
