Brumbies No.1 Blake Schoupp appeared to have dislocated his shoulder in the first two minutes of his return from an injury to the same joint in Perth on Saturday night.
He was thrown into the starting line-up in place of fellow prop James Slipper, who is battling an injury to his calf. It now looks likely Larkham will be without either man in his side's quarter-final next Saturday.
Brumbies captain Allan Alaalatoa was unsure about the extent of Schoupp's injury, but said he was confident his replacement Harry Vella would rise to the occasion in their do-or-die home clash with the Highlanders.
The injury put a dampener on an otherwise positive night for the Canberrans, who go into the finals with positive momentum, albeit disappointed they were unable to turn their most successful Super Rugby regular season in two decades into a top-two finish.
Both sides went into the match knowing they could do nothing to improve their ladder position, after the Melbourne Rebels' loss to the Fijian Drua ended the Force's finals hopes, while victories to the Blues and the Hurricanes consigned the Brumbies to third place.
But there was no chance Larkham was going to let his men go into the match without their collective foot firmly on the pedal.
Alaalatoa opened the scoring with a try in the sixth minute, before speedster Connor Toole doubled the lead with his eighth try of the season, outpacing his opposite number to run on to a perfectly placed Tom Wright kick.
Brumbies captain Allan Alaalatoa opened the scoring with a sixth-minute try against the Force. (Lukas Coch/AAP PHOTOS)
The Force heaped pressure on the Brumbies for long periods, but were often the architects of their own demise.
The visitors were solid in defence, but the Force were guilty of making simple errors in attacking positions to let their opponents off the hook.
They were let back into the game when Brumbies halfback Ryan Longeran was shown a soft yellow card shortly after the half-hour for interfering in a ruck. The Force immediately capitalised with a try through flanker Carlo Tizzano.
The Brumbies continued to defend staunchly in the second half and were more clinical in attack when given the opportunity to break forward.
Back-rower Luke Reimer impressed off the bench, forcing key turnovers with his intensity in the ruck when the Force threatened the Brumbies' tryline.
Toole's pace again came to the fore, recovering to make a try-saving tackle on Issak Fines-Leleiwasa, before breaking the Force defensive line to set up a try for fullback Wright.
Brumbies fullback Tom Wright (centre) scored a try in his side's victory over the Force. (Lukas Coch/AAP PHOTOS)
The Force scored consolation tries through Fines-Leleiwasa and George Poolman in the final minutes, but by that point both teams were no longer competing with all their heart.
Larkham rested several key men as the game petered out, including five-eighth Noah Lolesio and Alaalatoa, as he cast his gaze towards his side's clash against the Highlanders, who they vanquished 27-21 in Dunedin earlier in the season.
"The most important thing now coming into the finals is just make sure that we recover from this trip," Larkham told Stan Sport.
"We had a pretty strong game plan going into (the earlier game against the Highlanders), but they've evolved, they've improved as a team.
"We've identified a few areas where we think there's some opportunities, but we'll have a look at the game that they played this weekend and make some more assessments."
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