Michael Johnson says Fremantle players had great belief that their fitness work over the pre-season would carry them over the line against Port Adelaide on Sunday night.

Match report: Freo prevails in epic

Fremantle survived a finals-like duel against the side that knocked them out of last year's finals series at Domain Stadium.

They won by seven points having trailed by nine points five minutes into the last quarter.

"We knew going into that last quarter if we kept on chipping away and playing the way we have trained over the pre-season our fitness would kick in, and it showed," Johnson told AFL.com.au.

"It was just a gutsy win by the boys."

Showreel: Finals-like pressure

Johnson was especially pleased with his own fitness.

The 2013 All Australian defender missed last year's finals series after requiring surgery on his lower back.

He endured a very slow start to the pre-season before Christmas but has barely missed a beat since. 

Johnson, who is a potential unrestricted free agent at the end of this season, said he had great faith in the Dockers' fitness program and he was one of just two players to play every minute of Sunday night's epic.

"I ticked all the boxes after my surgery on my back," he said.

"When you go through a pre-season at Fremantle you really believe in the program that they give us. It has shown over the last few years that if you do the work over pre-season, come the season you should stand out amongst the group.

"I played 100 per cent game time today, which is good for me and hopefully I can just keep building on the fitness and my decision-making over the next couple of weeks." 

Freo travel to Simonds Stadium next Sunday to face Geelong.