Brumbies coach Dan McKellar found plenty to be pleased with in his side's 19-13 win over the Waratahs but he has his fingers crossed for young backrower Rob Valetini.
Valetini hobbled off the field in the 53rd minute with a knee injury, after the joint was twisted awkwardly in a maul, and the no. 6 was walking on crutches donning a brace post-match.
The 20-year-old has been cruelled by medial ligament injuries in the past two seasons and though McKellar could say it wasn't a repeat of that, he couldn't confirm a full prognosis.
"It was awkward - fingers crossed he just got a fright," he said.
"There's the potential to be some damage but not medial ligament, just assess him."
In better news, prop Scott Sio is expected to be fit for round six after coming off in the 43rd minute with a possible shoulder concern.
McKellar was proud of his side's defensive efforts against the Waratahs, with their line speed shutting down a star-studded Waratahs attack.
"Any football team you take away time and space and put them under pressure, it's hard to execute your skills," he said.
"I thought our backline in particular, they opened us up there early in the first half but after that our defence was very good."
It was the Waratahs who for on the score sheet first after Michael Hooper pounced on a Bernard Foley penalty that hit the posts.
Hooper leaped up to catch the ball after Foley’s shot deflected off the sticks and he withstood contact from Lochie McCaffrey and Tom Banks to crash over the line in just the fourth minute.
The inability to hang onto Hooper was possibly the only poor thing McCaffrey did all night, in a monstrous performance at no. 8.
It took the Brumbies just one crack off their lineout to score through Folau Faingaa, albeit this time the hooker was on the end of a string of passes that began in the lineout rathe than pushing the maul over, handing the hosts the lead in the 14th minute.
The Brumbies used their scrum to create another opportunity and only a desperate effort from Ned Hanigan stopped Lausi Taliauli from scooping up a clever grubber and scoring a near-certain try.
It was the Canberrans with all the momentum after a frenetic start from the Waratahs, with the sides barely venturing into the Waratahs attacking zone after that early try.
And the next time the Brumbies found themselves in scoring range Faingaa finished off a superb rolling maul to score his sixth of the season.
The Waratahs looked to their superstar backline to create some magic and a super Adam Ashley-Cooper pass set up a break for Kurtley Beale before Alex Newsome got his hands on it the Brumbies forced a penalty close to the line and that opportunity ended.
Just as the Waratahs began to build some momentum, a brain snap from Sekope Kepu turned things on their head with the tighthead prop sent to the bin for a dangerous cleanout on McCaffrey.
It was the Waratahs with the first score of the second half, almost nine minutes down, with some edge-to-edge work, including a slick ball from Israel Folau, putting Alex Newsome over.
The Brumbies replied less than five minutes later with a penalty try off another maul, with Waratahs prop Harry Johnson-Holmes sent to the bin as a result.
Foley managed to narrow the margin to less than a converted try in the 64th minute with a penalty, the only score from either side during Johnson-Holmes’ binning and the first Waratahs reward from a scrum.
It looked like the Brumbies had finally ignited their attacking fire in the 77th minute, with McCaffrey slipping through a Nick Phipps tackle attempt, throwing the ball on the boot and into space for youngster Mack Hansen to run onto.
While Hansen couldn't quite beat out Waratahs winger Alex Newsome, a favourable bounce landed right in front of replacement halfback Ryan Lonergan and the former Junior Wallabies captain duly pounced, but the TMO called a knock-on and it was back to a defensive scrum.
Appropriately, it was a Brumbies scrum that ended the game, with Christian Lealiifano eventually kicking into touch to seal the win, a moment reflective of the dominance upon which they built their game all night.
Waratahs coach Daryl Gibson was left to lament handling errors, partly caused by the Brumbies defence, and said there was work to do ahead of a huge clash with the Crusaders next Saturday night.
"With our ball control at crucial times in the econd half where we looked like we were really putting some nice phases together, just let ourselves down there," he said.
"The area that we're still lacking is our ball control and being able to really exert and hold the ball for long periods. On top of holding the ball, being really clever with our kicking off the back of that.
"Got to fix up the areas in our game that we need to continue to work on and we've got to go toe to toe with the Crusaders, they're the benchmark team right now."
The Brumbies move onto Queensland next week, to take on the Reds.
Tries: Faingaa 2, Penalty
Tries: Hooper, Newsome
Yellow Cards: Kepu (35’), Harry Johnson-Holmes (54’)