A CONTROVERSIAL non-decision in the dying stages of Sydney's two-point loss to Greater Western Sydney added even more sting to the visitor's loss on Saturday.

The Giants led by 21 points early in the third term before Sydney fought back and reduced the margin to three points when Isaac Heeney kicked his fourth goal late in the match.

The Swans bombed the ball forward with 40 seconds on the clock and Sam Reid looked to have dragged down a mark 20m out from goal, but the umpire called play on and the Giants bottled it up to force a stoppage.

GWS players held their nerve to secure a vital four points.

Replays showed some minor contact between Reid and his GWS opponent Jake Stein.

SWANS FALL SHORT Full match coverage and stats

Post-match, Sydney coach John Longmire didn't seem happy with the call, despite admitting that he hadn't had a chance to look at a replay of the marking contest.

"I don't know whether 'Reidy' got grabbed in the marking contest (or not), who knows," he said.

"I don't know if it was a mark or if anyone grabbed him by the arm, I don't know.

"I haven't spoken to him (Reid)."

WATCH John Longmire's full post-match media conference

The loss was the Swans' fifth in a row, with four of those defeats coming by 10 points or less.

Longmire said he can't fault the effort of his group, but the young side just isn't doing enough to compete with the competition's top teams for an entire match.

The second term, when the Swans gave up 5.1 to the Giants, and kicked just 1.4 themselves, came back to haunt them.

WATCH The gripping final two minutes

"We played well for three quarters and won three quarters of the game, but dropped away in that second and that’s what cost us in the end," Longmire said.

"We've just got to find a way to work through it and they’re lessons that are learned but they’re costly ones.

"We want to come off the ground and have the four points and have a win, and the feeling of a win.

"We are about winning, so we're disappointed that we lose.

"We're just short of that at the moment and over the stretch there’s been some tight ones heading back to the Essendon game, there's not been a lot in it.

"A call here or there either way and it can turn."