Walter Scott deservedly fired the home side in front after 25 minutes and they doubled their advantage early in the second half when Stynes latched onto a cross from Yacoub Mustafa and curled a superb shot home from just inside the box.
Stynes then took advantage of some sloppy Mandurah defending to make it 3-0 on 67 minutes before completing his hat-trick by capping off a superb team move with a composed finish.
And after the visitors lost Thomas Straker to a second yellow card, it was left to Callum Timmins to round things off in style two minutes before the end, finding the net at the second attempt having seen his initial effort blocked.
The display left Head Coach John Gibson understandably delighted, but he called upon his charges to show more consistency during the run-in to the end of the season.
“It was one of our most mature performances in a long time and we took our opportunities really well,” he said.
“But it shouldn’t take an apparent big game for us to want to do this.
“We’ll keep driving forward and the boys will get some confidence for the rest of the season.
“Stynes is a good player and did well today, but we’re very demanding of our group and we need to do more in the rest of year.”
The victory for Gibson’s side completed a clean sweep for Glory on the day, with the Under-18s winning 5-2 and the Under-20s also getting home 2-1.
Glory's youngsters return to action in a fortnight's time when they host Inglewood United.