New Zealand holders Waikato Chiefs finished top of rugby's Super 15 final season standings after surprise defeats for title rivals Northern Bulls and ACT Brumbies this weekend.

The Chiefs improved their chances of hosting this season's final next month with a 26-16 bonus-point win over a 14-man Auckland Blues at Eden Park on Saturday.

The Waikato team stayed top on 66 points after the Bulls crashed 30-13 to the Western Stormers in Cape Town to finish second, three points adrift. Both teams will have a bye when the first phase of the playoffs get underway next weekend.

The Brumbies botched their chance of finishing in the top two in a shock 21-15 loss to the lowly Western Force in Perth and they will host South Africa's Central Cheetahs in Canberra in next Sunday's qualifier.

Seven-time champion Canterbury Crusaders will have home advantage in the other playoff when they take on the 2011 winners Queensland Reds next Saturday.

The Crusaders ensured a home playoff with a nervy 25-17 victory over the Wellington Hurricanes in Christchurch on Friday.

The Reds clung on for a 14-12 win over the New South Wales Waratahs on Saturday to finish fifth ahead of the Cheetahs, who had a final round bye.

The Chiefs bounced back from their 15-43 defeat to the Crusaders the previous week, but they were made to struggle against an understrength Blues.

As if the long flight home from South Africa during the week was not enough of a handicap for the Aucklanders, they were further hamstrung in the 22nd minute when Kane Barrett was red-carded for stamping as they trailed 3-8.

With their season already over, the Blues could have given up but they increased the pressure on the New Zealand Conference winners to the final whistle.

The Bulls were fortunate that the Brumbies lost to the Force hours earlier after they went down to the Stormers.

The Pretoria-based Bulls had no answer to the brilliant attacking and defending of their long-time foes, and slipped to second in the final standings.

A bonus-point New Zealand derby victory for the Chiefs meant the Bulls needed to make it 10 wins in a row to remain on top, but they were always on the back foot from the kick-off.

Western Force stunned the Brumbies, scoring the first three tries of the match to post one of the major upsets of the season, notching just their fourth win to finish a tough campaign on a high.

Fortunately for the Brumbies, they had already booked their berth in the playoffs so the result did not have any significant repercussions, aside from dented confidence heading into the business end of the season.

In Christchurch, the Crusaders and Hurricanes scored three tries apiece but Dan Carter's goalkicking proved the difference with two conversions and two penalties to Andre Taylor's lone conversion.

The Reds needed a determined defensive effort in Sydney to survive as Wallaby back Berrick Barnes narrowly missed with a penalty attempt and botched a shot at drop goal after the final siren.

The Reds scrambled home on a try by Ben Lucas and three penalties from Quade Cooper. The Waratahs led 12-8 at halftime, but failed to score a point in the second half as Brendan McKibbin and Barnes missed four shots at goal between them to throw away an Australian derby victory.

In this weekend's other games with no playoff bearing, the Coastal Sharks scored 10 tries in a 58-13 romp over Southern Kings in Durban, while the Melbourne Rebels stormed back from 24 points down at half-time to nudge out the Otago Highlanders 38-37 in an astonishing recovery in Melbourne Friday.