Ruck-forward Justin Koschitzke personified a key difference between St Kilda and Fremantle in Friday night's massive AFL clash at Etihad Stadium.

Koschitzke was one of St Kilda's best as they withstood some first-class pressure from Fremantle and cracked them in the last quarter, pulling away for a 41-point win.

The result consolidated the Saints in the top eight, while the Dockers could lose eighth spot depending on other results this weekend.

Earlier this year, Koschitzke suffered plenty of scrutiny as he struggled for form.

But his coach Ross Lyon said Koschitzke was going through then what several Fremantle players are tackling - the desperate need to regain match fitness after an extended injury layoff.

By comparison, Lyon noted Fremantle's Michael Barlow looked set for a 40-plus possession game against St Kilda, but could not maintain that first-quarter effort.

Barlow missed the first half of the season and has only played four AFL games.

Lyon said Koschitzke had come off "an incredibly injury-interrupted five months post the grand final".

"As he's gotten fit, his form has come and funnily, that what happens with everyone.

"If you can get that depth of fitness and continuity, your talent shines through and that's really what's happening to Justin."

It is a point not lost on Dockers coach Mark Harvey.

Fremantle were superb at times against St Kilda - Lyon called them valiant - but eventually they were worn down and the Saints split them open in the last term.

"We've brought in a number of players over recent weeks who have had sustained periods out of the game," Harvey said.

"Whether we like it or not, that can compromise what we do in the last quarter.

"Then we have some younger players, so it's a bit of a dual effect ... I'm just talking reality and facts, that's all."

If St Kilda and Fremantle go on to make the finals, they will have earnt their spots.

The Saints face likely minor premiers Collingwood next week, followed by Sydney away, North Melbourne and Carlton.

Fremantle host top-four side Carlton, are away to North Melbourne, have Collingwood in Perth and then travel to play the Western Bulldogs.

While the Saints now have a six-game winning streak, Lyon said they must lift again to challenge the might of Collingwood.

"We've been practising pretty good effort, but I tell you what, we wouldn't want to play just two and a half quarters next week," he said.

The Dockers must win two of their last four to make the finals and Harvey, like Lyon, notes his team must lift.

"We get to find out whether we actually are a contender," he said.

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