Banfield booted four goals on Sunday, including three in a magical seven-minute blitz during the third quarter, to help the Dockers secure the 15.9 (99) to 13.7 (85) win in front of 47,214 fans.
Goalsneak Michael Frederick was also crucial with three second-half goals, while Rory Lobb took a series of powerful marks to finish with three majors.
Andrew Brayshaw (39 disposals, nine clearances) and Caleb Serong (31 disposals, six clearances) played huge roles in the midfield, and the experiment of playing Griffin Logue (seven marks, two goals) in attack continued to pay dividends.
Zac Bailey booted four goals for Brisbane and Charlie Cameron kicked three, while former Docker Lachie Neale finished with 31 disposals and four clearances in a strong display.
Banfield has technically played every game this season, but almost all of them have come as the substitute - either used or unused.
The 24-year-old made the most of his chances on Sunday in his 50-game milestone after being handed a rare spot in the 22.
Three of Banfield's goals were snaps.
His steadying goal in the final quarter when he scooped up the bobbling ball on the run before snapping truly was the most special of the lot.
Fremantle's victory came just eight days after they beat reigning premiers Melbourne at the MCG, with the Dockers (9-3) now a mere 4.1 per cent adrift of second-placed Brisbane on the ladder.
The Dockers trailed by 13 points at quarter time.
But Brayshaw's stunning 14-disposal second quarter helped turn the tide Fremantle's way, with James Aish (10 disposals, one goal), and Serong (11 disposals) also crucial in the fightback.
A pack mark from Lobb helped spark a run of three straight Fremantle goals, and tempers boiled over when Logue booted a major from the goalsquare.
Shirts were ripped and headbands lost as almost every player on the field converged to take part in the melee.
Tempers remained frayed for the remainder of the term.
The Lions lost Darcy Gardiner during the second quarter after he copped a painful hit to the ribs in a marking contest.
Logue committed an embarrassing blooper early in the third quarter when he tried to do the team thing by letting Travis Colyer's 45-metre shot on the run bounce through for a goal instead of taking an uncontested mark in the goalsquare.
The defender-turned-forward could only watch on as the ball bounced upwards on the goal-line and was promptly rushed through.
Fremantle recovered from that missed chance to boot six goals to three for the term, with Banfield nabbing three himself in a stunning burst.
The Lions closed to within 11 points early in the final term, but two clutch goals to Frederick, Banfield's snap on the run, and a long-range bomb from Lobb helped seal the deal.
Fremantle are set to be bolstered by the return of Nat Fyfe for Saturday's home clash with Hawthorn after the two-time Brownlow medallist made a successful comeback via the WAFL, while Matt Taberner and Michael Walters could also return.
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