Their success was however leavened by a potentially season-ending injury to former Wallabies captain David Pocock. Flanker Pocock, who missed most of last season with injury, had played only 13 minutes on Saturday when he was assisted from the field with a serious knee injury. The result of scans carried out after the match has not been released but there are fears Pocock suffered a ruptured ligament which will keep him out of Australia's series against the British and Irish Lions in June.
Pocock was replaced by 110-Test veteran George Smith, returning to Australian rugby from Japan, who played a larger part than expected in the Brumbies' victory by four tries to nil.
South Africa's Sharks also extend their unbeaten run to three games with a 21-12 win over newcomers the Southern Kings. But the Durban-based Sharks were unable to score a try for the second straight match and have now gone 194 minutes without a five-pointer.
The Pretoria-based Bulls also moved to a 3-0 record when they beat the previously-unbeaten Blues 28-21 on Sunday for their first win to date on Auckland's Eden Park.
In other matches, defending champions the Chiefs suffered their first loss of the season, going down to the previously winless Stormers 36-34 at Cape Town in a seven-try thriller.
Seven-time champions the Crusaders suffered their second straight defeat, conceding an intercept try seven minutes from fulltime to lose 29-28 to the Wellington-based Hurricanes. The Christchurch-based Crusaders are 0-2 for the season and struggling to advance their bid for their first title since 2008.
The Bloemfontein-based Cheetahs scored three first-half tries to shock the Highlanders 36-19, also leaving the Otago side without a win from two matches. The Cheetahs hadn't beaten the Highlanders in New Zealand since 1997 when current coaches Naka Drotzke and Os du Randt were members of a Free State team that won 49-18.
The Queensland Reds improved their record to 3-1 with a 23-13 win over the Melbourne Rebels, rallying from a 13-10 halftime deficit.
The Brumbies were among the most impressive winners in the fourth round, making their first 3-0 start to the tournament since 2005, the year after they last made the play-offs.
They now leave for South Africa where they will face the Sharks and Stormers without Wallabies Pocock and Pat McCabe, the latter still sidelined with a hamstring injury.
Brumbies coach Jake White said the severity of Pocock's injury was still to be determined.
"He is going in for a scan," White said. "These sort of players that play at this level understand when their body tells them something and he just feels it's not 100%.
"It shows you how fate plays out. It's just fantastic how things have worked out now that George has arrived."
The 32-year-old Smith is effectively playing with the Brumbies under loan and is due to return to his Suntory club in Japan in late May but an extension might be negotiated.
The Brumbies were in charge of the Waratahs by halftime with tries by captain Ben Mowen and flyhalf Christian Leali'ifano. Henry Speight scored the first try to sap a Waratahs' rally and Robbie Coleman added a length-of-the field try to clinch the Brumbies' first four-try bonus point since 2007.
"We're not going to get ahead of ourselves, but at the same time it's a massive game and that's the benchmark we've set," White said.
The Stormers celebrated their first home game by holding off the Chiefs 36-34 at Newlands.
The home team was never headed after posting the first points in the third minute with the first of fullback Joe Pietersen's eight-from-eight goalkicks. But they could never bury the relentless Chiefs, who trailed by as much as 13 points but were within two of the Stormers for the last 10 minutes.
An injury to Springboks winger Bryan Habana also tempered the Stormers' satisfaction in victory. Habana was stretchered from the field in the 55th minute, also with a knee injury, and will be sidelined for at least 10 weeks.
The Sharks relied again on the boot of Springboks flyhalf Pat Lambie, who nailed six penalties and a dropped goal, to beat the tenacious Kings.
Lambie's opposite, Demetri Catrakilis, kicked all four penalties for the Kings, who were even more impressive than in their win on debut over the Western Force. The Kings notched 107 tackles against the Sharks, missing only one against the 2012 finalists.
The Sharks had one try disallowed and were held up over the tryline three more times, boosting the confidence of the Kings.
Scrumhalf Sarel Pretorius scored two first-half tries for the Cheetahs who streaked to a 30-7 halftime lead over the bumbling Highlanders. The Highlanders put the opening kickoff in touch on the full in the first of a catalogue of errors that cost them the match.
Flyhalf Lima Sopoaga gave up tries from a charge-down and an intercept and was replaced after 37 minutes by All Black Colin Slade, playing his first match after a year-long injury break.
Springboks flanker Heinrich Brussow also made a return from a long injury layoff, playing the last 30 minutes for the Cheetahs.
The Crusaders seemed set for their first win of the season, off-setting last weekend's loss to the Blues, when tries to Israel Dagg and Dan Carter gave them a 28-19 lead midway through the second half.
But flyhalf Beauden Barrett closed the gap with a penalty -- maintaining a perfect kicking record from seven attempts -- and Leiua snatched the match away from the Crusaders with his late try. – Sapa-AP