ST KILDA coach Ross Lyon has admitted a late drop in composure and ball movement cost the Saints an upset victory over Sydney but chose to keep his deeper tactical critiques behind closed doors pending a full review.

Lyon’s comments followed a heartbreaking two-point thriller at the SCG, where a brave St Kilda performance went unrewarded.

SWANS V SAINTS Full match details and stats

Despite leading by 33 points in the second term and holding a 10-point cushion late in the match, the Saints could not hold off a fast-finishing Swans outfit. The hosts pulled off a stunning comeback, capped by the match-winning goal with just 15 seconds remaining to steal the game, 15.14 (104) to 15.12 (102).

"We played really well for the majority of the night. They really came home late," Lyon told reporters post-match.

"It's a game of centimetres, as opposed to inches. Inches is probably a bit long for what we experienced tonight; centimetres is probably about the right distance."

When asked if anything could have been handled differently in the dying minutes, Lyon pointed to the team's late execution.

"There's always a little bit of composure," he said.

"Things can be 50-50 calls, whether they are intercept marks or marks. But we just thought a little bit early, maybe, we just didn't use the ball as positively as we were in the first three quarters.

"So, we sent the messages to get that going. But I have to go away and review. Obviously, we've got some thoughts, but that's for internal consumption."

Meanwhile, Sydney coach Dean Cox praised his players' resilience after the gritty win, noting that the hard-fought victory will fuel the team's confidence in future.

"I said to the players at the start of the week and before the game that this was going to take the whole 120 minutes against a really disciplined, hard, contested, two-way running team. So, it took the whole 119 of them," he said.

"To the players' credit, at times when we were challenged, we rallied. We're starting to build a lot of belief that when we're in those positions, we can still get it done."

The win came at a cost, however, with defender Tom McCartin failing to finish the game following medical advice after a heavy knock.

The 26-year-old, who has a significant and concerning history of concussion issues, was forced from the ground following a crunching collision with opposing forward Liam Ryan early in the third term.

Although slow to his feet, McCartin was able to run off with the aid of trainers, but it was quickly decided he would take no further part in the match.

Given his background, the Swans will take a highly cautious approach to McCartin’s recovery timeline. Cox confirmed that because the defender was ruled out immediately, he bypassed a full Head Injury Assessment and entered straight into the League's concussion protocols.

"He's obviously disappointed, but he feels fine," Cox said of McCartin’s condition post-game.

"The doctors ruling him out was obviously the right thing to do, and now it's about trying to make sure that we look after his health. All reports (say) he's in great spirits at the minute, so that's the first thing, but we understand that he is concussed and we'll manage that accordingly."

Winger Justin McInerney was also subbed out at half-time with hamstring tightness, raising concerns after grabbing the back of his leg following a dribble kick in the second term.

"We'll determine the extent of that with scans tomorrow or Tuesday," Cox said of McInerney’s injury.

"Obviously, not finishing the game doesn't look great, so the extent and the severity will be known in the next few days."

Sydney's medical room was stretched even further late in the game, with Riley Bice (quad), Nick Blakey (ankle), and Callum Mills also picking up knocks. However, Cox played down any major concerns.

“They're okay. It's round 13 of a football season, where most of these guys have played every week. They're going to be sore, like every team, but they'll recover as well as they possibly can,” he said.

“We're six days away from Port Adelaide, which we can't wait for.”