While Stirling dominated proceedings in the first half, Gustavo Giron Marulanda netted a second-half brace along with substitute Paul McCarthy’s goal, giving the away team all three points.
Marulanda, who finished the 2015 season as top scorer and recently returned to Bayswater after a professional stint in Indonesia, booted goals at the 65th and 77th minutes.
The Lions came out of the blocks at their sparkling best, and dominated Bayswater for the majority of the first half.
Get in front of tomorrow's news for FREE
Journalism for the curious Australian across politics, business, culture and opinion.
READ NOWIn the 24th minute, a moment of individual brilliance and good fortune by young midfielder Lukas De Lima saw him open up the scoring for the Lions.
De Lima broke free in the middle and beat his man before playing a neat one-two with Steve Sokol and flicking his shot into the bottom right corner.
City opened up the game in the 51st minute, when Bor Bor Sam’s pin-point cross from the left found substitute Paul McCarthy in space in the box, heading home from close range.
City continued their electric start to the second half to draw level.
Jason Mirco’s initial effort was saved well by Perkins, but the rebound fell to Marulanda, who buried the ball.
After holding up the ball for some time at the left corner flag, substitute David Heagney crossed to Marulanda who was afforded too much time and space to slot home his second.
Despite both sides having late opportunities, Bayswater hung on and caused a significant upset for their hosts.
MORE: Cancer Council WA puts out call for therapist volunteers
MORE: Curtin Uni professor plays key role in Zika virus study
MORE: Scarborough businesses suffer as City scrambles to help