Legendary United striker Michelle Heyman's 56th-minute strike on Wednesday carried her side to the upset win and denied the Sky Blues the opportunity to become the first ALW team to win four straight premierships.

A win would have put them four points clear with a game to play before finals, although the margin remains at one heading to the weekend.

They'll get another crack at sealing the title when they host Melbourne Victory on Sunday, although it appears a much tougher ask than beating 11th-ranked Canberra.

The loss leaves the door open for second-placed Melbourne City, who play Perth after Sydney's match.

Canberra, who are embroiled in a turbulent period with governing body Capital Football unable to confirm their future beyond this season citing increasing operational costs, looked up for the occasion in their final home game of the season.

They took Sydney's punches in an 11-shots-to-two first half, before clinical second-half substitute Heyman seized her moment.

The recalled Matilda was on the spot when Sydney custodian Jada Whyman spilled a shot from teammate Vesna Milivojevic, taking her time before tucking the ball home.

It was a cutting-edge the Sky Blues lacked, particularly when dominating the first half.

Cortnee Vine came closest to breaking the deadlock, her placed effort on 12 minutes forcing a diving save from Canberra keeper Chloe Lincoln who tipped the ball onto the outside of the post.

The pair's duel continued later in the first half when Vine's rushed shot through a sea of bodies somehow found its way into Lincoln's hands.

Heyman should have made it 2-0 in second-half stoppage time but found the post with a one-on-one effort, although the miss didn't hurt her side.

It was Canberra's second consecutive clean sheet, after somewhat remarkably going the first 19 games of the season without keeping one.

Australian Associated Press