Adrian Zahra scored an 86th-minute winner for Melbourne Heart to defeat Sydney 1-0 on Thursday evening, condemning the Sky Blues to bottom spot at Christmas after four consecutive defeats.

Lavicka told FoxSports after the game he would remain positive about the champions' top six aspirations.

"I am naturally a positive person. It is mathematically still a chance to be there and we will fight to the last moment but we must start to be more productive in attack and don't make crucial mistakes at the back."

He added about the contest: "(It's) Frustration for us because we allowed them to pick up some points but without the goals there's more chance to lose it."

Victorious Heart coach John van 't Schip admitted his side needed an ounce of luck to win Thursday's contest.

"Today we were a little bit lucky, especially the second-half," he said.

"The first-half we played well, the second-part of the first half we were dictating but the second-half we struggled.

"Then you need a bit of luck and all this season we've missed the luck and today it was there, so we're very happy."

Van 't Schip also hailed the impact of substitutes Gerald Sibon and Zahra who combined for the late winner.

"That's why they're on the bench, to try and bring some new fresh blood," he said. "And I think they did that.

"It was a good move from Gerald, he has the feet to do that and the vision. Adrian has the quick run and it was good finish."

Heart are now fifth and host North Queensland Fury in their next match on January 2.

Van 't Schip added: "Every game that we play now is like a final."

Sydney, on the other hand, are next in action on December 29 away to Adelaide United.