The Waratahs have soared to the top of the Super Rugby ladder and won the Australian conference with an emphatic 39-8 bonus-point win over the Brumbies.
But the Waratahs' club-record-equalling fifth straight victory came at a heavy cost on Saturday night, with captain Dave Dennis suffering a suspected season-ending knee injury.
Dennis was helped off ANZ Stadium with a reported torn anterior cruciate ligament after falling awkwardly on his right knee following a tackle on Brumbies winger Henry Speight in the 35th minute.
The former Wallabies flanker has already had two knee reconstructions and it would be a cruel blow if the 28-year-old was ruled out for the rest of the Waratahs' campaign to have a third operation.
The Waratahs are leading the competition with two rounds remaining and are assured of their first finals appearance in three years after putting the injury-ravaged Brumbies to the sword and then seeing the Western Force thumped 40-14 by the Blues.
But stand-in skipper Michael Hooper admitted Dennis' injury soured celebrations.
"It's horrible. Denno's been our leader from the front this year. You never like to see that," Hooper said.
"But the boys carried on and put it out there for Denno in the second half.
"We said we wanted to be top two at the start of the the year and we're on track to do that."
Needing to win to retain control of their own finals destiny, the Brumbies entered the pivotal derby with 11 players, including six Wallabies, unavailable.
Their woes were compounded in the opening minutes when Test centre Tevita Kuridrani was forced off following a head knock.
Injuries, though, weren't the Brumbies' only concern, with their lineout a shambles. Fourth-choice hooker Ruaidhri Murphy - a specialist prop - had four throws stolen in the first half alone and another after the break before being hooked.
The lineout wobbles and ill-discipline at the breakdown handed the Waratahs almost 70 per cent of possession and the home team inevitably made the Brumbies pay.
With driving assistance from fellow prop Sekope Kepu, loosehead Benn Robinson opened the scoring with the game's first try in the 16th minute.
An intercept try to winger Alofa Alofa three minutes later - off a loose Speight pass - doubled the hosts' advantage, with five-eighth Bernard Foley slotting both conversions.
The Brumbies gave themselves hope in unlikely fashion when fullback Jesse Mogg outleapt former AFL player Israel Folau to score from a cross-field kick from Christian Lealiifano.
After the two sides traded early penalty goals in the second half, the Brumbies were still in the hunt, trailing 17-8 before some Folau magic turned the match.
The dual-international beat about half a dozen defenders and carried three over the line after a powerful 40-metre burst, only to be denied a try by the video referee. No matter, though, with Foley converting the pressure into seven points when he strolled over shortly after.
Alofa clinched the bonus point with the Waratahs' fourth try before powerhouse No 8 Wycliff Palu iced the big win with a well-deserved five-pointer in the dying seconds.
While the Waratahs can secure Australian conference honours - and most likely a home final - next Sunday with victory over the Highlanders at Allianz Stadium, the Brumbies' finals fate now rest with others.
With a bye offering the ACT outfit no competition points next weekend, the Brumbies will likely slip out of the top six entering into the final round.