Goals from supersub Adrian Segecic and Patryk Klimala helped Ufuk Talay's side secure victory in front of 8002 at Campbelltown Sports Stadium on Saturday.
Sydney moved into sixth with the result but could slip out of the finals places depending on the outcome of Sunday's clash between Western Sydney Wanderers and Perth Glory.
The meeting between Macarthur and Sydney shaped as potentially season-defining for both clubs but the home side could not lay a glove on the Sky Blues.
Mile Sterjovski's side had just one shot on target throughout the entire match, which came courtesy of rightback Kealey Adamson in the 86th minute.
Macarthur lacked any attacking spark and their season is on the brink of implosion, having picked up just one win in their last six games.
On New Year's Day the Bulls sat second but they now find themselves in eighth spot.
Their collapse in form comes soon after the club allowed captain Valere Germain, striker Ariath Piol and winger Jed Drew to move overseas in the January window.
Germain's replacement up front, Harrison Sawyer, struggled to make an impact with limited service in a lifeless first 45 minutes.
The second half began with much greater intensity, Macarthur goalkeeper Filip Kurto doing fantastically well to palm two shots from Sydney's star import Douglas Costa away in the space of 90 seconds.
Costa also rattled the crossbar but the Bulls failed to heed the warning with Joe Lolley slipping a well-timed ball into the path of Klimala who fired beyond Kurto's reach in the 58th minute.
Any hope Macarthur had of getting back into the contest quickly evaporated when Kurto passed a goal-kick to mid-season signing Kevin Boli.
The defender hesitated at the back and a quick-thinking Segecic was hot on his tail.
Boli fluffed his clearance and Segecic was able to turn the ball back into the Macarthur net for his eighth ALM goal of the campaign.
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