Kerr was in scintillating for for the home side finding the back of the net early in the second stanza to level the scores before nodding home in the final five minutes to secure the win and move her team to the top of the W-League ladder.
Blazing temperatures in Perth meant players were given two drinks breaks each half but it didn't stop the visitors from taking the lead after 25 minutes.
Matildas defender Alanna Kennedy demonstrated yet again her incredible set-piece ability with a sublime curling effort from the left edge of the 18-yard box to make it 1-0 for the visitors.
Perth clicked into gear after conceding and Kerr would've given them the lead late in the opening 45 if it wasn't for some quality saves from Sydney FC shot stopper Aubrey Bledsoe.
Kerr came back after the interval with intent and found the back of the net with a thunderous header in the 47th minute off a looping corner kick.
Sydney stopped what appeared a sure Glory goal in the 61st minute after a Kerr breakaway with a last ditch challenge.
With the game looking like it would end a draw, Kerr stepped up in the 85th minute to nod in a Rachel Hill cross and secure a crucial three points for the Bobby Despotovski coached side.
The result moves Perth to the top of the standings after seven games, while Sydney remain in fourth.
