Sydney showed plenty of fight to hold off a late surge from the Roar, despite being a player down, after setting themselves up with their dynamic first-half performance.
Longo’s cracking effort and a brace from Sam Kerr proved enough for Sydney, while Brisbane’s goals came from Emily Gielnik and Vedrana Popovic.
Brisbane opened the scoring before Longo, just five minutes later, collected a short corner wide on the left, turned, and curled a shot into the top right corner of the goal for a well-deserved equaliser.
Sydney were lucky to hold on after former Football Ferns striker Emma Kete was red-carded by referee Kirralee Gardner with 13 minutes to go following an off-the-ball incident.
Sydney go through to the grand final while Brisbane will miss out on the privilege for the first time in Westfield W-League history.
In the second semi-final match up the Melbourne Victory booked a spot in the grand final alongside Sydney after a 4-3 penalty shootout victory over Perth Glory at nib Stadium.
Both sides were locked at 1-1 at the end of extra-time despite several chances for either side to take the lead.
Perth took the early lead in the penalty shootout when Kaitlyn Savage saved Caitlin Friend’s shot.
It then came down to Jessica McDonald to win it with the final penalty for Melbourne, which was saved by Savage in goal.
However, referee Katie Patterson ordered a retake for Savage coming off her line and McDonald slotted home the second chance to put Victory through to the decider.
The W-League grand final will be held on Sunday January 27 at AAMI Park between Melbourne Victory and Sydney FC.
The grand final will feature semi-final goal scorer Annalie Longo and Hannah Bromley for Sydney, while their teammate Emma Kete will be sidelined following her red card on Sunday. Fellow Kiwi Rebekah Stott is expected to feature for Melbourne.