The Brumbies scored 35 unanswered points in the second half to clinch a record win over the beleaguered Waratahs.
Noah Lolesio returned from two months out with a torn hamstring to inspire the Brumbies to glory over the Reds in the Super Rugby AU final.
The ruthless Brumbies scored five tries to see off Western Force and ensure they will be at home in the final on September 19.
The Brumbies came unstuck in the rain at Leichhardt Oval, where the Rebels scored four first-half tries.
The Brumbies were victorious once again in Super Rugby AU, though left it late to see off the Reds in Canberra.
The Brumbies are the only team to have won every Super AU game after they were too strong for the Western Force.
The Brumbies made it two wins from two in Super Rugby AU as a late try from Issak Fines saw them beat the Waratahs.
The Rebels came up short with a second-half fightback as the Brumbies ran in five tries in a 31-21 Super Rugby AU victory.
After a three-month suspension due to coronavirus, Super Rugby will return in Australia from July 3, albeit in a revamped format.
SANZAAR chief executive Andy Marinos has described reports over potential alternatives to Super Rugby as "merely speculative."