Gustavo Giron Marulanda scored twice with Andrija Jukic and Bor Bor Sam adding the others to lift the hosts a point behind leaders Inglewood United with two games remaining.
Despite the win, Bayswater coach Chris Coyne was keen to ensure his team maintained their high standards in the remaining games.
“I’m obviously pleased with the result and the effort, but I thought we had to be a lot more professional and a lot more clinical than we were today,” he said.
“We will just keep doing what we are doing and hope that someone slips up. It was Perth’s turn today so we have to keep winning games and hope someone gets a result off Inglewood.
“Inglewood have been a very good team and have been up there all year so credit to them, but that doesn’t mean we’re not going to keep pushing to win the title.
“We have a tough game against Mandurah next week, so all we can do is worry about ourselves, work hard and hope the result will come.”
Armadale coach John O’Reilly blamed his side’s defeat on a lack of depth and an inability to take chances.
“In the last few weeks I think we have been creating a lot of chances,” he said.
“But the difference between being at the top of the ladder and the bottom comes down to working those opportunities into actual goals.
“We had a really good run of defensive performances at the start of the year, but unfortunately now we have been hit with some end of the season blues with injuries and suspensions.
“So I think our defensive woes come down to a lack of depth to finish as strongly as the first-half of the season.”
In other matches on Saturday, Sorrento defeated fellow top four contenders Floreat Athena 2-0 with a Sean Canham brace at Percy Doyle Reserve, while Joondalup United put a dent in Perth SC’s chase for successive champion titles after a goalless draw at Dorrien Gardens.
ECU Joondalup claimed a 2-0 win over Mandurah City at Securitas Protect Stadium, Subiaco beat Perth Glory 2-1 at Ashfield Arena, Alex Tanevski netted a brilliant hat-trick as Stirling recorded a 3-1 win over local rivals Balcatta at Grindleford Reserve, and Inglewood United defeated Cockburn 2-0 to remain on top of the ladder.