The Waratahs looked set to claim their first victory in five outings against Australia's 2018 and 2019 conference winners only to concede a gut-wrenching try four minutes from fulltime.

Replacement halfback Issak Fines late game-breaker extended the Brumbies' winning streak to six matches over Australian opposition stretching back to a loss to the Queensland Reds in March last year.

It was also extremely cruel on Rob Penney's rebuilding Waratahs, who dominated for much of the match on Saturday night having been humbled 47-14 by the Brumbies in the very last game before Super Rugby was suspended in March because of COVID-19.

But the Tahs paid dearly for conceding two tries in three minutes just before halftime after opening up a 20-5 lead.

"Very disappointing that," said Waratahs captain Rob Simmons.

"I think as a forward pack we really fronted up, stopped that maul, they got through there once which was disappointing and we led most of that game until the end there. That's what footy is; winning those pressure moments. We let one slip and that's what happens."

Brumbies coach Dan McKellar was mightily relieved after watching his side overcome the first-half loss of injured five-eighth Noah Lolesio and Wallabies prop James Slipper, who failed a HIA.

"The Tahs were very good, a good young side. I take my hat off to them and you feel for them, to be honest. It was a tough slog," McKellar said.

Despite the defeat, classy young five-eighth Will Harrison and NSW's new-look front row of returning Wallaby Tom Robertson, starting debutant Tom Horton and Harry Johnson-Holmes were standouts.

Earmarked as potentially the Wallabies' next No.10, Harrison set up a beautiful try for winger James Ramm and slotted three penalties and two conversions for a 13-point personal haul.

His head-to-head tussle with fellow former Australian under-20s star Lolesio only lasted half an hour before Lolesio limped off with a hamstring injury.

It was a tough blow for the Brumbies, who only 15 minutes earlier lost Wallabies prop James Slipper after he failed a HIA.

The visitors had a ready made replacement in Test star Scott Sio but it didn't stop NSW's remodelled front row from dominating at scrum time.

The Brumbies turned down a gift three points early, opting against taking a penalty goal attempt from right in front and the gamble paid off.

Instead Tom Cusack opened the scoring with a try in the fifth minute after Harrison spilt Lolesio's cross-field bomb straight into the flanker's arms.

Harrison atoned with two penalties to edge the Waratahs ahead 6-5 as the home team gained the ascendancy when Horton finished of a driving maul while Brumbies down to 14 men after winger Andy Muirhead was yellow-carded for a deliberate offside.

The Brumbies' night threatened to go from bad to worse when Lolesio departed but quickfire fire tries to hooker Folau Faingaa and flanker Robbie Valetini meant they trailed by just three points at the break.

Harrison extended NSW's advantage to six shortly after halftime but will rue not slotting another eight minutes from fulltime that probably would have sealed the deal for the Waratahs.

Australian Associated Press