An injury-time goal to substitute Troy Hearfield rescued A-League leaders Central Coast Mariners and dealt a massive blow to Sydney's finals campaign, with the NSW derby finishing 1-1 at BlueTongue Stadium on Saturday.
A close-range strike from youngster Joel Chianese 10 minutes into the second half put Sydney ahead.
The Mariners created several chances in the last half hour, with Hearfield darting in to put a header past Sydney goalkeeper Ivan Necevski.
Central Coast have a three-point lead with three rounds remaining, while Sydney are three points behind sixth-placed Newcastle, who beat Melbourne Victory earlier on Saturday.
The stumbling Mariners have won once in their past six games.
Rookie Chianese scored his second goal in four games, firing home from close range after he was initially foiled by Coast goalkeeper Matthew Ryan and Nicky Carle had a shot blocked by Trent Sainsbury.
The late equaliser was a tonic for a Mariners side facing a punishing schedule with their first Asian Champions League match against Tianjin Teda in China on Wednesday followed by a game in Perth next Sunday.
Chianese's goal came in the middle of a strong Sydney push early in the second half, with Scott Jamieson clipping the crossbar just after the break.
The Mariners created some good opportunities in the last half hour, with veteran midfielder John Hutchinson rattling the crossbar and lively substitute Bernie Ibini prominent.
Ibini was off target with two efforts and had a cross headed over the bar by an unmarked Oliver Bozanic.
Both teams struggled to create much in the early stages, as they battled to string together passing movements on the slippery rain-soaked pitch.
Carle had a shot blocked by Ryan and emerging Mariners midfielder Tomas Rogic had a curling shot pushed away by FC custodian Ivan Necevski, who also dealt with a close-range header form Adam Kwasnik.
The NSW derby featured some rugged challenges with one shuddering clash between Terry McFlynn and Bozanic and first-half yellow cards to Sydney's Rhyan Grant, Karol Kisel and Jamieson and second-half bookings for Hutchinson and Mariners' team-mate Josh Rose.
"We played against a very good Sydney team tonight, a Sydney team that were desperate with their top six chances on the line and we had to really dig deep tonight," said Mariners coach Graham Arnold.
"I felt we deserved a point. I think we had as many good chances as they did and I thought that their goal was offside.
"The character of the boys showed again, it was fantastic," added Arnold, who said Sainsbury wouldn't travel to China because of concussion.
Sydney coach Vitezslav Lavicka felt his team played well, but rued the latest in a series of late goals conceded by his team.
"Normally when we pick up a point against the leader it's quite positive, but we all know that we needed more than one point tonight," Lavicka said.
"The boys did well, they played well. We controlled the game, especially the first half, early in the second half as well. We created chances. We didn't take the result."
McFlynn said Sydney needed to win all three of their remaining games to have a chance of making the finals.