Triple champions Northern Bulls and holders Waikato Chiefs can lock up the top two positions -- and with them, semi-final hosting rights -- in this weekend's final Super 15 regular round of matches.
The Bulls will take a big step towards hosting this season's Super Rugby final if they can win their South African derby against the Western Stormers in Cape Town to finish top after 20 rounds of the southern hemisphere provincial series.
The Pretoria-based Bulls are two points clear of the Chiefs, who face a tricky New Zealand derby with the Blues in Auckland if they are to maintain their top two spot heading into the playoffs.
The top two teams have a bye from next weekend's opening playoffs and will face the winners in the following week's semi-finals to decide this season's Super 15 finalists.
Only Australia's ACT Brumbies, a former two-time winner, and, mathematically, the seven-time champions Canterbury Crusaders, can knock the Chiefs out of the top two places in final round jockeying.
The Brumbies, resuming after a month's break for Australia's home Test series against the British and Irish Lions, take on Western Force in Perth on Saturday where they have only lost once in four trips, while the Crusaders host the Wellington Hurricanes.
The Bulls, who have lost on two of their last three trips to Cape Town, have Francois Venter in for injured midfielder Jan Serfontein, and Jano Vermaak taking over from injured scrum-half Francois Hougaard.
The suspension of Wilhelm Steenkamp opened the door for 19-year-old Jacques du Plessis, who could make his debut for the Bulls after he was included as replacement lock.
Captain Dewald Potgieter said the Bulls will have to step up their approach and execution if they want to beat the Stormers and finish the season top of the heap.
"We did not react well in certain situations when placed under pressure last weekend and will have to improve on that," Potgieter said.
"The Stormers have momentum and the home crowd on their side and this being the big North/South derby we will have to front up. It is fair to say that this will be our biggest test this season."
Springbok captain Jean de Villiers has recovered from his sternum injury, and will lead the Stormers after missing the last two wins over the Cheetahs and the Kings.
Record-breaking Springbok winger Bryan Habana will be playing in his final and 57th match for the Stormers, having scored 18 tries in the process.
The Chiefs have made several team changes with prop Toby Smith starting and Liam Messam returning after a back injury. Robbie Robinson and Lelia Masaga are on the wings and Tim Nanai-Williams (centre) and Andrew Horrell (fullback) have been named.
"We are obviously pretty disappointed with our performance last week but we are excited about the opportunity to redeem ourselves," coach Dave Rennie said. "We know the Blues will want to put in a big performance in their final game of the season."
Wallaby flanker George Smith will be on the bench with Colby Faingaa starting in the number seven jersey for the Brumbies, who have been boosted by the return of seven Wallabies from national duty for the match against Force.
Crusaders coach Todd Blackadder has made only one change, putting Tom Donnelly at lock with Luke Romanof out with an ankle injury against the Hurricanes in Christchurch.
Prop James Slipper will captain the Queensland Reds in the injury absence of Wallabies James Horwill and Will Genia in Saturday's Australian derby with the NSW Waratahs in Sydney.
The Reds cannot be overhauled in the top six but this weekend's game gives playmaker Quade Cooper a chance to show what the Wallabies missed after he was passed over by former coach Robbie Deans for the Lions series.
In this weekend's other games with no playoff bearing, the Rebels face the Otago Highlanders in Melbourne and the Sharks host the Kings in Durban.
The sixth-placed Cheetahs have the bye.