IT HAPPENED the last time Fremantle played Sydney. And again in the Dockers' win over Geelong.

The Dockers' ability to dominate stoppage must be contained by the Swans if Dean Cox's side is to book a Grand Final spot, according to three-time Brisbane premiership captain Michael Voss.

Fremantle scored a season-high 76 points from stoppage in its semi-final win over Geelong, and 50 against the Swans in round 18.

Speaking on AFL.com.au's Finals Film Room alongside Essendon champion Matthew Lloyd, Voss highlighted how metres gained from stoppage had become a crucial metric for the Dockers.

"Everyone knows about the clearance game, but what's valued with coaches and also teams behind the scenes is the metres gained from stoppage," the former Carlton coach said.

"When Fremantle are going very well, this is the stat that they dominate.

"You see the game on the weekend, Fremantle versus Geelong. In the first half, when Fremantle had it their way, they just dominated from stoppage, not just from clearance, but their efficiency and their damage from the clearance. 

"They had 1,537 metres gained to Geelong 736 – plus 801 metres gained. But it was their ability to be able to hit the scoreboard, which was the outcome. 

"If you go to the second half, Geelong were able to neutralise it. Fremantle still kicked their five goals, but the important thing was Geelong kicked seven, four of them from centre square bounce."

Voss outlined a similar impact when the Dockers and Swans met in round 18, when Fremantle was held to 0.11 in the first half before kicking 15 goals after the main break on its way to a 38-point win.

In that game, the Dockers were held to 512 metres gained from stoppage in the first half (and a score of 0.2), before exploding for 1,644 metres gained in the second (and 7.0).

"The last time that they played Sydney, they were able to dominate the exact same stat," Voss said.

"In the first half, Sydney really boxed on around the clearances. They denied entry from those clearances, which was the important stat, and therefore Fremantle weren't able to score. 

"But you see the second-half dominance. This is where Fremantle got their surge. They really took the game away from Sydney (and) absolutely dominated the metres from stoppage. 

"They went in nine out of 10 times. You aren't going to stop Fremantle if you give that up. And they were able to kick seven goals."