Lewis Jetta's last-quarter speed showcased the potential of the new AFL substitute system as Sydney beat North Melbourne on Saturday by one point.

Jetta was subbed on early in the last quarter and had a major impact, setting up his team with scything runs down the Etihad Stadium wing.

One of those runs set up a crucial goal to Adam Goodes.

Late in the match, Jetta also used his pace to lay a game-saving tackle on Michael Firrito.

"I just said to myself `when you get out there just run them off their feet and try to make a big impact to try and win the game'," Jetta said.

"I pretty much did that."

But Jetta nearly did not play, with his ordinary form putting him under the selection microscope this week.

Rather than drop him, the Swans decided to use Jetta as their substitute in a "burst" role and the ploy worked brilliantly.

"We discussed what to do with him this week, because he's a really exciting player, we want him confident and back in our team," Swans coach John Longmire said.

"But we thought the sub option for us ... this week, on a pretty quick deck, coming on in the last quarter, hopefully he could do something.

"He was pretty good in that last quarter ... he did what we wanted him to do and he gave us that real lift off the bench."

During one of Jetta's scything runs, he was nearly out of bounds and North sub Ben Speight was hot on his tail, practically touching him - but never quite catching up.

Then came the Firrito tackle, the sort of defensive action that ends up on highlight footage.

"As soon as we got back in here (change rooms) a lot of the boys said it was a match-winning tackle," Jetta said.

"I just tried to do the team thing to keep the pressure up."

Jetta pulled up sore from the tackle, but was able to play out the game.

"We've been talking about how his run offensively is so important, but how that can be used as a weapon defensively as well," Longmire said.

"Some of the best quick players in the competition, their speed with the ball is fantastic, but it's what they do when the opposition have the ball that really makes opposition ball movement nervous.

"It was a good step forward when he did that today."

Brought to you by AAP © 2024 AAP