Macarthur became the top dogs in the harbour city with a gripping 1-0 A-League derby win over a 10-man Sydney FC on Sunday afternoon.
Bouncing back from last week's 4-1 thumping by Western United, the Bulls shot to second on the A-League ladder with their fifth win of the season.
The statement was even more significant for the league newcomers, who ensured the Sky Blues suffered their first back-to-back defeats of the season.
Bulls striker Matt Derbyshire continued his prolific season with his seventh goal from 10 games when he tapped in a shot from Spaniard Markel Susaeta, who danced through confused defence to set up the lone goal in the 36 minute.
The match reflected what is shaping as a passionate rivalry between the two Sydney clubs. Paulo Retre's red card in the 38th minute drew parallels to their last derby a month ago when Bulls skipper Mark Milligan was marched early on and the Sky Blues shot to a 3-0 win. But in Saturday's return match, Retre's studs up challenge on Bulls defender Jake McGinn put the hosts down to 10 men from 38 minutes in. The midfielder's boot connected with McGinn's thigh earning him a debatable early shower.
It was a moment of contention for the Sky Blues and coach Steve Corica was booked for saying so from his spot on the Netstrata Jubilee Stadium sideline.
Up to then Corica's men had spoiled all of their chances with both Retre and striker Kosta Barbarouses unable to land shots in the first half.
Typically for this entertaining A-League season, Retre's red card wasn't the only controversial moment.
Earlier, Bulls defender Alec Golec was not booked for an obvious deliberate handball but was later yellow carded for a challenge on Alex Bauhmjohan in the 24th.
Milligan also escaped punishment for a swinging arm shot on Barbarouses midway through the first half.
But with just 10 men in the second half, Corica's men couldn't rally late.
They'll get a chance to bounce back against Brisbane on Saturday, while the Bulls will travel to Gosford to face ladder leaders Central Coast on Monday week.