A memorable goal from captain Mitchell Duke and a mighty rearguard effort allowed Western Sydney Wanderers to end their drought against Sydney FC and go top of the A-League table.
Duke's unstoppable flying 19th minute header from near the penalty spot from a Daniel Georgievski cross settled a pulsating derby, which threw up plenty of talking points.
The defending A-League champions had far more chances but two crucial second-half VAR calls went the Wanderers way.
The visitors were adamant they had equalised in the 51st minute through a Kosta Barbarouses header, but the VAR ruled the whole of the ball hadn't crossed the line.
A few minutes later the VAR cleared a possible handball by Keanu Baccus, and Wanderers held out to earn a 1-0 win.
The first Sydney derby at Bankwest Stadium attracted a crowd of 28,519 who produced a tremendous atmosphere.
It was Wanderers' first win over the Sky Blues in seven league games and almost three years, and only their second in the last 17 competitive contests between the two clubs.
Steve Corica's side piled up the chances but couldn't find a way past the Wanderers' Swiss goalkeeper Danile Lopar.
The veteran custodian stopped attempts from Milos Ninkovic and Adam Le Fondre in the first half and foiled Kosta Barbarouses in a one-on-one in the second.
In the first half, a short-range dink from Ninkovic hit the crossbar and teammate Rhyan Grant hit the woodwork just before halftime, but was ruled offside.
Right at the death, former Sydney FC defender Matt Jurman denied his old side with a great block when Ninkovic looked certain to score.
Wanderers defended with tremendous resolve, while the visitors will rue a costly attempted backheeled clearance by left back Paulo Retre, which the home team used to set up the deciding goal.
As expected, former Wanderers' playmaker Alex Baumjohann got a hostile reception from the home supporters, getting booed when he went to take three early corners in front of end where the home club's active supporters group was situated.
Although he had plenty of ball the German was unable to make a major impact and was replaced in the 71st minute.
The derby had the occasional flashpoint but referee Alireza Faghani brandished yellow cards after a couple of scuffles.
He booked both Nick Sullivan and Ryan McGowan after a push and shove in the first half and the Sky Blues' Rhyan Grant and Western Sydney midfielder Pirmin Schwegler following a second-half skirmish.