BSS/AFP) - South Africa are firm favourites to wrap up a second straight Rugby Championship title for the first time when they face Argentina at Twickenham on Saturday in a competition with an uncertain future.

This year`s tournament has been one of the most exciting and unpredictable since Argentina joined South Africa, New Zealand and Australia in the southern hemisphere competition in 2012.

The Springboks top the table by a single point heading into the sixth and final round of matches this weekend.

A bonus-point victory against the Pumas in London would guarantee the world champions the title regardless of the result in Perth between Australia and New Zealand earlier on Saturday.

The All Blacks can still emerge victorious if results go their way, though South Africa have a huge points-difference advantage. Australia are rank outsiders.

South Africa will go into the match at Twickenham, technically a "home" game for Argentina, buoyed by their 67-30 demolition of the Pumas in Durban last week and expecting plenty of support from a sizeable expatriate community.

Springboks coach Rassie Erasmus admits his team will be in the fortunate position of knowing what they need to do when they take to the pitch.

But he warned the final score in Durban flattered his men and expects a "big fightback" from Argentina.

"Last week they were in the running to win the title, and they`ll be determined to make up for that result, so we are expecting them to throw everything at us on Saturday," he said.

"They may be out of the title race, but they have beaten the All Blacks, Wallabies, and British and Irish Lions this season, and it would be a big target for them to defeat us as well."

Erasmus has made one change to his starting XV, with the fit-again Ox Nche returning at loose-head prop.

Sacha Feinberg-Mngomezulu stays at fly-half after the 23-year-old scored a Springbok-record 37 points in a match during a sensational display last week.

- All Blacks dream -

All Blacks coach Scott Robertson has not given up hope of wrestling the title back from South Africa.

"Get up for the match, doesn`t matter who we`re playing, where we`re playing, so there is an opportunity this weekend," he said.

Australia, for whom James Slipper will be playing his 151st and final Test, are desperate to snap a 10-game losing streak against the All Blacks.

"They will be hugely motivated," warned Robertson. "Been a while since they`ve beaten us, there`s a little bit of hype around them, so it`s going to be a hell of an occasion."

Despite the compelling drama, there is uncertainty over the future of the Rugby Championship.

Next year New Zealand are set to tour South Africa for a series billed as the "Greatest Rivalry" -- the first traditional tour involving rugby union`s historic superpowers for three decades.

South Africa are expected to make a return visit four years later.

Complicating the picture, a new Nations Cup is being launched in 2026, bringing together the northern hemisphere teams that make up the Six Nations, the four sides in the Rugby Championship and most likely Japan and Fiji.

The rejig of the international calendar means there is expected to be no official Rugby Championship next year, with doubts over future editions.

Other matches could still take place, such as Bledisloe Cup fixtures between Australia and New Zealand.

Erasmus admitted he was unsure how the dust would settle.

"I know next year is the `Greatest Rivalry` and the touring of New Zealand," he said.

"I`m not in a board room so I don`t know exactly how it will work. We love playing against Argentina and against Australia and I`m not quite sure how that`s going to work out."