Pretoria - The Bulls did not even need to play to remain top of the Super 14 standings after a series of upsets stalled the leading contenders in the fifth week of the annual southern hemisphere competition.
The Bulls, who face the Hurricanes next Friday, are now the only unbeaten team in the competition after their South African counterparts the Sharks and Australia's Waratahs both suffered surprise defeats.
Australia's Reds threw abandoned traditionally cautious style to open up an 18-6 lead by halftime against the Sharks, which they held on to notch a 25-13 victory against the pre-competition favourites.
The Waratahs also suffered their first loss of the year when they were upended 21-11 by the Brumbies in a feisty encounter on Friday.
Both teams finished battered and bruised, with Brumbies captain Stephen Hoiles ruled out of the three-match tour of South Africa with a knee medial ligament strain.
"Steve's been very strong for us this season and he will be a loss particularly as captain of the side, for which he's done an outstanding job," coach Andy Friend said.
"Fortunately one of the strengths of the side this season is our depth and we're in a fortunate position to be able to bring someone of Mitch Chapman's calibre and experience into the squad."
Super 14 champions the Crusaders, who are missing several players through injury, blew a comfortable 20-6 lead against Australia's Western Force and only just held on for a 23-23 draw at Lancaster Park on Saturday.
The Crusaders, who had a core of experienced players and coach Robbie Deans leave at the end of last year's Super 14 are missing All Blacks captain Richie McCaw and are a lowly 11th on the table.
McCaw suffered a knee injury in last week's loss to the Highlanders and will not be back until mid-April.
The Highlanders were unable to repeat that winning performance when Chiefs wing Leila Masaga beat four defenders down the touchline to give his side the lead for the first time and a 14-10 victory in Invercargill.
New Zealand's Blues shrugged off a 35-31 loss to the Sharks in their previous fixture to run in six tries and thrash South Africa's Cheetahs 46-12 at Albany.
The Cheetahs are the only side in this year's competition yet to win a game, while the bonus point victory for Auckland propelled them into the top four.
The Stormers prepared for a five-week road trip to Australia and New Zealand by scoring eight tries in thrashing fellow South African side the Lions 56-18 in Cape Town.