FREMANTLE forward Chris Mayne says his side needs to focus on what made it a top-four contender early in the season and rediscover its defensive edge after back-to-back losses.

Fremantle lost its first Western Derby since round three in 2007 on Sunday, with the rejuvenated West Coast out-pressuring Mark Harvey's side all over the ground to gain a 51-30 edge in inside 50s and win by 33 points.

Mayne, one of the competition's best defensive forwards, said Fremantle needed to get back to the game style that had given it a 4-1 start to the season, starting against Port Adelaide at AAMI Stadium on Sunday.

"It's for us to keep building morale, keep getting around each other and focus on the stuff that we've been good at - our pressuring, our forward pressure and our contested ball and hard-ball gets," Mayne said from Fremantle Oval on Monday. 

"It's unfortunate that we've been playing the way we have the last two weeks, but it's something for us as a group to get back on track and bounce back."

Fremantle, which lost to Richmond by 49 points in round seven, has slid to eight spot on the AFL ladder after consecutive losses.  

Mayne said coach Harvey's message to the players after the match on Sunday was quiet and the group would review the game on Monday afternoon. 

Hayden Ballantyne (hamstring) was withdrawn before the match and replaced by first-year player Jayden Pitt, and Mayne said the side missed the goalsneak's presence.    

"It's disappointing not to have 'Ballas'," he said.

"He's a great asset to the side with his forward pressure, tackling and niggling attitude.

"We had other players step into his role (and) we're confident in the depth that we've got.

"It's just for those players to stand up when they get the opportunity."

The inside 50 differential was the most alarming aspect of Fremantle's performance on Sunday, with limited opportunities for Mayne (two goals) and fellow forwards Kepler Bradley (one) and Jack Anthony, who was held goalless in his Fremantle debut.

"West Coast worked really hard. They had a good defensive [approach] around stoppages and were able to get the ball inside their [forward] 50 a lot more," Mayne said.

"For us to not get the ball down there, it's definitely disappointing, but we've got to find out where we can improve in that."

Nathan Schmook covers Fremantle news for afl.com.au. Follow him on Twitter: @AFL_NSchmook