The Springboks moved top of Pool B on 15 points with a 49-18 triumph in their final match at the Stade Vélodrome in Marseille, bouncing back from a 13-8 defeat to world number one-ranked side Ireland on September 23.

Second-placed Ireland have 14 points and third-placed Scotland 10 going into the teams' clash in Paris on Saturday (October 7).

Only an unlikely three-way tie on 15 points through a Scottish bonus-point victory and Irish bonus-point defeat would put South Africa at risk by deciding the pool on points difference.

An early penalty from William Havili put Tonga into a 3-0 lead, but a fifth-minute try from Cobus Reinach followed by the first of four successful conversions from Handré Pollard set South Africa on their way.

Canan Moodie and Deon Fourie also crossed the whitewash for South Africa before Ben Tameifuna gave Tonga a lifeline just before half-time with a try to reduce the deficit to 21-8.

Jesse Kriel found the all-important fourth try for South Africa to earn the bonus point, before Manie Libbok took over successful kicking duties for tries from Willie le Roux, Marco van Staden and Kwagga Smith with the last action of the match.

Fine Inisi and Patrick Pellegrini contributed unconverted tries for Tonga in an entertaining second half, but could not prevent a third defeat of the World Cup for their team.

In the day's early match, Australia played what is expected to be their last fixture of the tournament at the Stade Geoffroy Guichard in Saint-Étienne, and ran out 34-14 winners against a valiant Portugal.

Defeats to Wales and Fiji appear to have put paid to Australia's hopes of extending their stay in France and have them on course for their first-ever pool-stage exit, but the Wallabies climbed to second on 11 points in Pool C after their final match.

Fiji are a point behind in third, and will reach the last eight at the World Cup for the first time since France 2007 unless they lose to Portugal next Sunday (October 8) in Toulouse.

Third-place in the pool earns an automatic qualifying place at the next World Cup in 2027.

Ben Donaldson opened the scoring with a fourth-minute penalty for Australia, but they found themselves behind to a seventh-minute try from Pedro Bettencourt converted by Samuel Marques.

However, Bettencourt was then sin-binned for a high tackle on Izaia Perese, and Australia took full advantage with tries from Richie Arnold, Dave Porecki and Angus Bell all converted by Donaldson to lead 24-7 at the break.

Fraser McReight in the 47^th minute sealed the bonus point for Australia, before Rafael Simões grabbed Portugal's second try converted by Marques when playing against 13.

An unconverted Marika Koroibete try for Australia completed the scoring.

The pool stage is due to finish next Sunday, with the next Rugby World Cup match scheduled for Thursday (October 5) in Lyon, where three-time winners New Zealand are hoping to effectively seal a place in the quarter-finals against already eliminated Uruguay.