PERTH found the 334 target set by Rockingham-Mandurah a mountain too big to climb on Saturday in its Premier Cricket match at Lark Hill.
After slumping to 3-25, a 101-run partnership between Luke Jury (86) and Sean Roberts (53) gave the Demons some hope, but batsmen perished as the run rate required climbed.
Second Grade had some nervous moments but a fine 73 by Jack Baker secured the win.
Third Grade lost whilst Fourth grade won outright.
First Grade have the destiny of their season in their hands in the final fixture, a One Day match against Mt Lawley on Saturday at Fletcher Park.
The equation is simple, a victory will see a spot in the finals.