The Force ended their Super 14 campaign on Friday beating the Brumbies by 29 points to 22. The result was the first victory that the Force enjoyed over an Australian team in 2008.
Both teams scored four tries and it was the first time ever in an Australian derby that both teams scored the bonus point try.
He inspired the comeback and along with his own try he had a hand in two others and kicking three conversions and a penalty to guide Force to victory.
Both teams went into the last-round encounter with 6-6 records and on 28 competition points, out of contention for the semifinals.
With the result, Force will finish eighth and the Brumbies ninth.
The tries came in chunks at Subiaco Oval, with the Brumbies scoring the first four and the Force scoring the next four in a stretch of 29 unanswered points.
When Adam Ashley-Cooper scored in the left corner in the 26th minute, the Brumbies secured a four-try bonus point and a thrashing looked inevitable.
Francis Fainifo scored twice inside the first 20 minutes and flanker George Smith sent Mark Gerard and Ashley-Cooper over with floating cut-out passes as the Brumbies attacked at all opportunities.
And if Stirling Mortlock had been on target with the boot and landed more than one from four kicks, the buffer would have been even greater.
"It was a tale of two halves, you can't explain it," Mortlock said.
"We went out with the intent of executing and going direct, and we did that in the first half.
"Unfortunately, the Force got a sniff just before half time ... they were too good in the end."
After six battering phases, 17-year-old center James O'Connor crossed for his maiden Super rugby try to get the Force on the scoreboard seven minutes from halftime.
That galvanized the Perth-based team.
O'Connor and Giteau combined to give Josh Tutu space and the center ran 25 meters and dived over in a cover tackle to start the second-half scoring.
Then Giteau split the defense with a solo run from the quarterline and swandived over untouched, then converted from in front to make it 22-19 in the 49th minute.
Scrumhalf Chris O'Young snuck over after a series of forwards had peeled off the back of a close-range maul to give the Force a lead after Giteau had chased and tackled Gerard and forced a turnover on the tryline.
Giteau converted to make it 26-22 with 20 minutes remaining and then landed a penalty from in front to extend the margin to seven points in the 64th minute.
"We probably played 20 minutes of the ugliest rugby we've played and then 60 with good intensity," Force captain Nathan Sharpe said.
"At one stage it was 22-zip, and to put 29 unanswered points on the Brumbies is no easy feat.
"To come in at half time and turn that around, that stands us in really good stead for seasons to come."
Pen - Matt Giteau
Subiaco Oval, Perth
Referee: Paul Marks (Australia)/Nathan Pearce (Australia)
Assistant referees: Ian Smith (Australia), Grant MacNeill (Australia)
TMO: Geoff Acton (Australia)
Assessor: Scott Young (Australia)
1. Pek Cowan,2. Tai McIsaac,3. Troy Takiari,4. David Pusey,5. Nathan Sharpe (c),6. Matt Hodgson,7. David Pocock,8. Richard Brown,9. Chris O’Young,10. Matt Giteau (vc) ,11. Haig Sare,12. James O’Connor,13. Josh Tatupu,14. Dane Haylett-Petty,15. Cameron Shepherd
Reserves 16. Luke Holmes,17. Kieran Longbottom,18. Sitaleki Timani,19. Sam Wykes,20. James Stannard,21. Scott Daruda, 22. Junior Pelesasa
1. Nic Henderson 2. John Ulugia 3. Guy Shepherdson 4. Alister Campbell 5. Mark Chisholm 6. Mitchell Chapman 7. George Smith 8. Stephen Hoiles 9. Patrick Phibbs 10. Christian Lealiifano 11. Francis Fainifo 12. Tyrone Smith 13. Stirling Mortlock (c) 14. Adam Ashley-Cooper 15. Mark Gerrard