The Brumbies will host the Cheetahs in a play-off in Canberra
The Force put ended their season on a high when they beat the Brumbies 21-15 in their Australian derby in Perth.
The defeat means that the Brumbies will host the Cheetahs in a play-off in Canberra next week after finishing the season in third place on the standings.
Anchored near the bottom of the ladder, the unfancied Force scored the first three tries of the match to post one of the major upsets of the year, notching just their fourth win to finish a tough season on a high note.
It was a bad night for the visitors from the very outset, as they put the ball into touch on the full from the kick-off in a portent of what was to come.
They looked to have a slim chance of stealing the win when the Force's Jayden Hayward missed a penalty in the 80th minute, but Matt Toomua inexplicably forgot to ground the ball before passing it forwards to a teammate to resume play.
That handed a scrum feed to the grateful Force, who had two potential tries turned down by the video referee, under the posts and they kicked the ball out as soon as they gained possession.
Brumbies captain Ben Mowen said the result was a timely wake-up call for the Brumbies.
"We didn't play good territory all game and our kicking really let us down," he said.
"The Force were extremely enthusiastic and played the conditions well.
"They played smart footy and exposed us. It is probably a really good wake-up call for us going into a finals campaign.
"We are fortunate we have another chance to play next week."
Mowen said the Brumbies still believed they could win the Super Rugby title.
Force skipper Matt Hodgson was thrilled his team finished the season positively, especially with some players turning out for the team for the last time.
"We put it in for the full 80 minutes tonight and we had a belief," he said.
"We had nothing to lose and we wanted to finish on a high note."
The Force started superbly, with Hodgson and Ben McCalman running in first-half tries as the home side took a 14-3 lead into the break.
They extended that lead in the 47th minute, when Junior Rasolea capitalised on a line break from Nick Cummins to score his first Super Rugby try.
The Jayden Hayward conversion had them ahead 21-3 and they looked in total control.
However, the Brumbies struck back through tries to Tevita Kuridrani and Scott Fardy to narrow the deficit to 21-15 in the 66th minute.
With Hugh McMeniman stretchered off, the Force looked vulnerable, but were able to hold the Brumbies at bay as the visitors paid for their handling errors.
For the Force:
Tries: Hodgson, McCalman, Rasolea
Cons: Hayward 3
For the Brumbies:
Tries: Kuridrani, Fardy
Western Force: 15 Jayden Hayward, 14 Patrick Dellit, 13 Ben Jacobs, 12 Junior Rasolea, 11 Nick Cummins, 10 Sias Ebersohn, 9 Alby Mathewson, 8 Ben McCalman, 7 Chris Alcock, 6 Matt Hodgson (captain), 5 Hugh McMeniman, 4 Sam Wykes, 3 Kieran Longbottom, 2 James Hilterbrand, 1 Pek Cowan.
Replacements: 16 Ben Whittaker, 17 Salesi Ma'afu, 18 Toby Lynn, 19 Richard Brown, 20 Brett Sheehan, 21 Sam Norton-Knight, 22 Sam Christie.
Brumbies: 15 Jesse Mogg, 14 Henry Speight, 13 Tevita Kuridrani, 12 Christian Lealiifano, 11 Joe Tomane, 10 Matt Toomua, 9 Ian Prior, 8 Ben Mowen (captain), 7 Colby Faingaa, 6 Peter Kimlin, 5 Sam Carter, 4 Scott Fardy, 3 Ben Alexander, 2 Stephen Moore, 1 Scott Sio.
Replacements: 16 Siliva Siliva, 17 Ruan Smith, 18 Fotu Auelua, 19 George Smith, 20 Robbie Coleman, 21 Andrew Smith, 22 Mark Swanepoel.
Referee: Rohan Hoffman (Australia)
Assistant referees: Ian Smith (Australia), Damien Mitchelmore (Australia)
TMO: Matt Goddard (Australia)