Hyundai A-League leaders Adelaide United have added to Sydney FC's misery, producing a late winner to sink the Sky Blues 2-1 at Allianz Stadium.

The game appeared headed for a draw until Dario Vidosic struck in the 88th minute to condemn Sydney to their fourth straight defeat before a small crowd of just over 13,000.

Earlier, Yairo Yau seemed to have ensured the home side at least a point with a goal just before the hour to cancel out Fabio Ferreira's 21st minute opener.

But the Reds spoiled those plans with a reply two minutes from time.

Nigel Boogaard smacked his drive against the crossbar, the rebound falling to Evan Kostopoulos who took an ugly air swing.

The ball landed at Vidosic's feet and he hit a sweet shot into the bottom left corner of the net.

Adelaide could justifiably claim justice was served after they had what looked a perfectly legitimate goal cancelled out after just 14 minutes.

Marcelo Carrussca worked a lovely one-two with Jeronimo to score, only to look up and see the linesman flagging him for offside.

Replays suggested it was the wrong call but Adelaide didn't have to wait long for reward.

Ferreira eventually gave Adelaide the lead with his first A-League goal.

Vidosic produced an exquisite back heel flick to the unmarked Ferreira and he let fly with an unstoppable drive to beat Ivan Necevski at the near post.

The Reds were good value for their lead but the Sky Blues did carve out a number of opportunities.

As usual Alessandro Del Piero was at the centre of most of them, the Italian almost beating Eugene Galekovic with a dipping free kick right on half-time.

Del Piero, marking the 20th anniversary of his professional debut, continued to produce some sublime touches in the second half but his team-mates were unable to capitalise.

When Sydney's goal did finally come, the architect was an unlikely source.

Pascal Bosschaart's 40m ball out of defence put Yao in a one-on-one foot race with Iain Fyfe - and there was only ever going to be one winner.

Yao's speed allowed him to shrug off Fyfe and enter the box alone before firing a right-foot shot past Galekovic for a deserved equaliser.

But there was one final twist left, Vidosic putting another nail in Sydney's fast faltering campaign.

There was some good news for the Sky Blues, with ex-Socceroo Jason Culina playing the final 23 minutes in his first game for almost two years.

Sydney FC 1 (Yau 57)
Adelaide United 2 (Ferreira 21, Vidosic 88)
Bet365 Man of the Match: Dario Vidosic

Crowd: 13,317