John van 't Schip's men, maddeningly inconsistent from week to week, have a reputation for turning up when local bragging rights are at stake and they did nothing to dispel that notion on Saturday, demonstrating to a packed AAMI Park what they are capable of but so infrequently produce.
Equally typically, it was a lack of cutting edge that nearly prevented City from claiming all three points, while Victory only have themselves to blame after failing to reach their usual high standards for the second week in succession.
Paartalu struck in the 91st minute, powering home a header from Mate Dugandzic's cross to spark scenes of wild celebrations.
"The boys were really good in their way of working and fighting," said Van 't Schip.
"I think we deserved the win. Winning a derby is nice."
Perth Glory capitalised on Victory's slip-up later on Saturday, beating Central Coast Mariners 4-1 at home to open up a six-point advantage at the top of the table.
Two goals in the space of three first-half minutes from Chris Harold and Andy Keogh put the leaders in control.
Matt Simon pulled one back for the Mariners early in the second half but Perth were not to be denied and added a superb third goal through teenager Daniel De Silva before Harold struck again with 12 minutes remaining.
