Celtic went down 1-0 to Pirates in the league last Sunday, and will aim to bounce back with interest when they battle Bidvest Wits for TKO honours at Princess Magogo Stadium in KwaMashu on Saturday (18h00).
"The mood is good, it's positive," said Jelusic, who is in his first season with Phunya Sele Sele.
"All the players are very motivated. We might have lost the game [against Pirates] but it didn't make anything negative to our squad.
"It's a very important thing for us. It's a cup final, it's big motivation for us and the players. We are preparing to give our best to this game and try achieve the best result in this cup."
The Serbian has earned recognition for reviving Siwelele's fortunes after their brush with relegation last term.
He added: "There are some changes of course but I think even in the previous season the club had very good players. The players we had last season contributed very much this season together with the new players we have this season. To be in a cup final is motivation to all of us and especially for the players."
Jelusic took over the Celtic reins in July from caretaker boss Lehlohonolo Seema, who guided the club with John Maduka after the dismissal of Serame Letsoaka in October 2016.