The Eagles lost in-form midfielders Daniel Kerr (adductor) and Andrew Embley (hamstring) during the warm-up, but overcame the losses courageously to win 14.12 (96) to 9.9 (63) and move into the top eight.
It was West Coast's first Derby win since round three, 2007, and Fremantle coach Mark Harvey's first loss to Eagles counterpart John Worsfold since taking the reins late in 2007.
West Coast took its highly effective forward press to another level on Sunday and used it to dominate the second quarter and open up a 37-point half-time lead.
In a near perfect 30-minute display of pressure football, the Eagles won the inside 50s (15-4), contested possessions (38-33) and clearances (12-7), kicking five goals to one for the term.
They maintained their pressure for the majority of an accomplished four-quarter performance and laid a season-high 82 tackles.
Matthew Priddis gave the Eagles their midfield edge with 27 possessions and a game-high six clearances, and was unanimously voted the Ross Glendinning medallist as best afield.
Fremantle ruckman Aaron Sandilands had 45 hit-outs, but he was beaten on the day by West Coast pair Nic Naitanui and Dean Cox, who combined for 39 hit-outs and set up a 41-35 clearance edge.
The Eagles had fortunately held young runners Brad Sheppard and Andrew Gaff out of the WAFL on Saturday and both were required after the dramatic warm-up saw Kerr and Embley withdrawn.
Despite the losses, West Coast started brighter and was only challenged for a brief period early in the final quarter, when David Mundy and Kepler Bradley kicked back-to-back goals to trim the margin to 21 points.
Mundy (28 possessions and a goal) and Fyfe (28 and two) were Fremantle's best performers, with the team's middle-tier failing to lift after Harvey's challenge last week.
Meet the press
West Coast's forward press has been hailed this season, but it's a game plan that has been in the works since the end of the 2008 season when strategy and innovations coach Phillip Walsh came onboard from Port Adelaide. With the team's youngsters maturing and its veterans adjusting to the new style, West Coast appears to be pressuring sides as well as anybody right now. They won the inside 50 count 51-30 and held it there for long periods.
Influential players
Priddis continues to be underrated outside the Eagles' camp and among some supporters, but he is putting together an ultra-consistent season and making the midfield players around him better. He won 17 of his 27 possessions in contests and his clearance work is a key to launching the side's forward press. He was aided by the ruck work of Naitanui and Cox, who went forward to kick a goal each.
Once the ball was inside 50, Eagles forwards Jack Darling, Quinten Lynch and Josh Kennedy worked tirelessly to keep it there. Even Mark LeCras, not known for his defensive pressure, impressed in this area. Kennedy set up the first of LeCras' two goals, a 45m snap, with his defensive pressure, giving the Eagles their 37-point half-time lead.
Key match-up
Former Collingwood forward Jack Anthony made his Fremantle debut on Sunday opposed to wily premiership full-back Darren Glass. Service was poor for the key forward, with Fremantle going inside 50 just 30 times for the match, but he had five possessions and was held goalless nonetheless. Glass won a series of important one-on-one contests in the third term when Freo made a brief run.
Magic moment
Skilful Fremantle midfielder Nat Fyfe is a natural right-footer, but you wouldn't have known watching him kick one of the great Western Derby goals, late in the third quarter. The 19-year-old ran towards the boundary in the forward pocket and kicked a left-foot checkside goal under pressure that should be considered one of the goals of the year so far.
What it means
West Coast not only moves back into the top eight with a 4-3 record, it looks capable of staying there. Fremantle slides to eighth spot and continues to be served by too few. David Mundy, Nat Fyfe and Aaron Sandilands predictably stood out, with Matthew Pavlich being used in a midfield role to cover injuries to key players Michael Barlow and Anthony Morabito. Freo has put in two poor performances in a row and needs to regain confidence against Port Adelaide.
Betting
West Coast was a favourite with the tipsters pre-match, but it was an even-money game with the bookies. Ballantyne's expected withdrawal didn't shake the market, but Embley's hamstring injury pre-match tipped the odds in Fremantle's favour. When the in-form Kerr (adductor) injured himself in the warm-up, Fremantle was installed $1.86 favourite with Betfair, to West Coast's $2.12.
The next four
West Coast: The derby win leads into a winnable home game for the Eagles against the Western Bulldogs (Patersons), before taking on Collingwood (MCG) and then Gold Coast (Patersons) and Adelaide (AAMI).
Fremantle: Fremantle now has the opportunity to gain some momentum with two winnable games before two tough opponents, beginning next week against Port Adelaide (AAMI), then St Kilda (Patersons), Hawthorn (MCG) and Essendon (Patersons).
Dream Team highlights
West Coast: Matt Rosa ($340,800), Quinten Lynch ($267,900) and Nic Naitanui ($250,200) were the Dream Team stars for the Eagles with 104, 102 and 100 points respectively while Scott Selwood's ($320,900) 99 and first-year player Jack Darling's ($254,300) 77 were good value.
Fremantle: David Mundy ($425,500) and Nat Fyfe ($377,100) had big games for Fremantle with 116 and 114 respectively to continue their solid seasons.
West Coast 4.1 9.5 10.9 14.12 (96)
Fremantle 2.1 3.4 6.5 9.9 (63)
GOALS
West Coast: Kennedy 3, LeCras 2, Nicoski 2, Darling 2, Lynch, Masten, Cox, Naitanui, Shuey
Fremantle: Mayne 2, Fyfe 2, Crowley, Pavlich, Johnson, Mundy, Bradley
BEST
West Coast: Priddis, Naitanui, Lynch, Rosa, Darling, S Selwood, LeCras, Glass
Fremantle: Fyfe, Mundy, McPharlin, Sandilands, Pavlich
INJURIES
West Coast: Andrew Embley (hamstring) replaced in selected side by Brad Sheppard, Daniel Kerr (groin) replaced in selected side by Andrew Gaff
Fremantle: Hayden Ballantyne (hamstring) replaced in selected side by Jayden Pitt, Ryan Crowley (quad)
SUBSTITUTIONS
West Coast: Patrick McGinnity replaced by Andrew Gaff at three quarter-time
Fremantle: Nick Lower replaced by Jayden Pitt in the third quarter
Reports: Nil
Umpires: McBurney, Kennedy, Armstrong
Official crowd: 40,567 at Patersons Stadium
The views in this article are those of the author and not necessarily those of the AFL or its clubs
