With a group of supporters cheering them on, Mandurah ran on with a strong team.
A huge effort from both teams lead to a good start to the game, then Mandurah pushed ahead, taking the early lead.
Mandurah continued scoring, Bryn Pou and Jezza Kasuas crossing the line for some amazing tries in the first half.
The second half started off slower, with Kalamunda pushing back.
Mandurah were unable to stop the attack and Kalamunda crossed the line,.
With the final whistle ready to go, Tyson Parkes scored an incredible intercept try to seal the game, with Mandurah winning 25-7.
Next week, the B grade will play their grand final at McGillivray Oval in Mt Claremont, taking on Cottesloe at 1.30pm.