Wellington - The Bulls and Crusaders' joint lead atop rugby's Super 14 tournament will come under threat in the 11th round as their closest rivals meet to press bids for the semi-finals.
The Stormers and Reds meet in Brisbane on Friday in a match between third and fourth-place teams. On Saturday, the fifth-place Waratahs and sixth-place Brumbies meet in Sydney to press their claims for the playoffs.
The Waratahs start the match one point outside the top four, while the Brumbies are four points adrift.
Below those teams, the fight for playoff places has become more desperate and brutal. The seventh-place Blues, who play the ninth-place Sharks in Durban on Saturday, and the eighth-place Hurricanes, who meet the Highlanders at Dunedin, are both battling to sustain fading playoff hopes.
The Bulls and Crusaders each have 34 points, although the Crusaders holds the higher rung on the ladder on points differential.
The Crusaders meet the Force in Perth on Friday at the start of a three-match road trip, while the Bulls return to their home ground in Pretoria after playing their last four matches in Australia and New Zealand.
In the other weekend match, Chiefs hosts the Bloemfontein-based Cheetahs on Friday.
The Bulls completed their road trip with a 2-2 record, beating the Force and Chiefs but losing to the Blues and Reds. Those results dropped them from first place and they have difficult matches remaining against the Stormers and Crusaders.
The defending champions will take some solace from the fact that three of their last four games are at Pretoria's Loftus Versfeld where they are unbeaten in 15 games.
They face the easiest of their last four matches on Saturday against winless compatriots the Lions, but coach Frans Ludeke said no match is easy at this time of the season.
Ludeke has made only two changes to his starting lineup for Saturday's match, replacing the injured Fourie du Preez at halfback with fellow Springbok Heine Adams and naming Jaco Pretorius at centre in place of Stefan Dippenaar.
He said although the Bulls and Johannesburg-based Lions are separated by 12 places in the championship standings, the outcome of Saturday's match was not a certainty.
The Lions are desperate to post the first win of their season.
"We are also in a desperate situation. It's close and nobody is safely in a semi-final spot just yet," Ludeke said. "We still need to make the cut. That is why this game is still massive for us."
The Crusaders have been strengthened for their match against the Force by the return of star flyhalf Dan Carter and fellow All Blacks Kieran Read, Brad Thorn, Zac Guildford and Owen Franks.
Assistant coach Daryl Gibson said the return of Carter was crucial as the seven-time champions face a tough run-in against the Force, Stormers, Bulls and Brumbies.
"We know we've got some big games coming up and champion players really do come to the fore," Gibson said. "Really, watch this space and watch Dan Carter do his business."
The Cape Town-based Stormers remain the form team of the competition after wins over the Blues and Chiefs and are the side best-placed to supplant the Bulls or Crusaders in the top two.
Stormers captain Schalk Burger said his team was ready for a tough test from the Reds.
"We've focused a lot on maintaining the standards set in the wins over the Blues and Chiefs and executing the game plan for the Reds, which doesn't differ all that much but needs to be done with the same efficiency," Burger said.
Reds coach Ewen McKenzie has made one change to his side for the match, naming Adam Byrnes at lock in place of the injured Van Humphries.
"This is the fifth South African side we'll have faced in as many weeks and each of the last four had particular strengths," McKenzie said.
"The Stormers combine elements of all four of those, so Friday is a bit like a final exam for all the work we've done over the past four weekends."