Sunday's game at McGillivray Oval was locked at 10-10 at halftime, but the Force scored 13 unanswered points after the break.
Lack of discipline proved a massive problem for Fijiana Drua, who were down to 13 players for 10 minutes of the second half and played just over 45 minutes with 14.
Flanker Nunia Uluikadavu was given a yellow card in the 18th minute and another in the 34th, while reserve hooker Keleni Marawa was binned in the second half.
Force were more consistent and efficient in the set pieces and Fijiana Drua showed only glimpses of their renowned attacking flair.
Western notched successive Super W wins for the first time and the victory lifted them one spot to fourth above the Brumbies, who they play in a momentous final round home clash at HBF Park next Saturday, with the winner guaranteed a top four spot.
"Belief is a big thing. We're riding the momentum of winning now. We're still learning how to win. I think we've just got to ride this train until it runs out," Force captain and centre Trilleen Pomare told Stan.
"For us (next week's game) is a must win. We know that's our grand final. The momentum of these two weeks leading into next week is what we needed."
Fijiana Drua, who remain third, one point ahead of the Force, posted first points when star fullback Lavenia Tinai crossed following some great support play featuring multiple offloads.
The Force replied in the 20th minute with flanker Leah Miles diving over in the corner.
She was set up by impressive winger Martha Mataele, who notched her own five-pointer a few minutes later to give the Force their first lead.
The irrepressible Tinai levelled the scores following a quick tap.
Force dominated possession and territory early in the second half, but an inability to finish their opportunities allied to stout Fijiana Drua defence kept the scores level.
A 52nd minute penalty to five-eighth Nicole Ledington edged the Force ahead.
Ledington extended the lead to 10 points five minutes later when she converted after lock Libya Teepa burrowed over after a scrum close to the line.
The Force five-eight added a last minute penalty to complete the scoring.
Fijiana Drua finished on the wrong end of a 24-11 penalty count.
"The girls lacked a lot of discipline this game," Fijian Drua captain and prop Bitila Tawake told Stan.
"I guess the Force wanted the win more than us, our attack let us down."
Fijiana Drua are away to second-placed Queensland next Sunday.
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