The Springboks ran in seven tries to Tonga’s three to nab a crucial bonus point to leave them atop Pool B on 15 points.
The two teams who will advance to the quarter-finals will be decided when the world’s number one ranked team Ireland - who beat the Boks last week - take on Scotland, ranked fifth, in Paris on Saturday (Oct 7).
A win for Ireland would see them finish in top spot and South Africa as runners-up.
However, should Scotland beat Ireland by a margin of 21 points or more, with both teams scoring four tries to earn an attacking bonus point, that would mean all three teams would finish pool play on 15 points.
That permutation would see the Scots topping the group on points difference ahead of Ireland, in second spot thanks to their better head-to-head record against the Boks, in third.
“We’ll have to wait,” said Boks coach Jacques Nienaber. “Our pool gets sorted out on Saturday so it’s a waiting game.
“The key thing for us was to get the win first and then to get a bonus point and then obviously to try to get as many points as we could to put ourselves in the position to get out of our pool.”
Nienaber added: “The reality is that where we are currently, I think between ourselves, Ireland and Scotland everybody can still miss out on the quarter-final, every single team, all three of those teams.
“The pool will only be decided on Saturday.”
The Boks had just one job to do againt Tonga, a bonus-point victory, and tries from Cobus Reinach, Canan Moodie, Deon Fourie, Jessie Kriel, Willie Le Roux, Marco van Staden and Kwagga Smith ensured that.
Pollard ticks boxes
There was also a welcome return for Handre Pollard after a 13-month absence, the fly-half kicking all four of his conversion attempts.
“It’s brilliant to get 50 minutes into his legs, get exposed to international rugby - it’s a big stepping stone for him and we can build from there,” Nienaber said.
“He got some time in against a proper Tonga side. I think he will get better. He was solid. The fundamentals we wanted him to tick the boxes of, he ticked them.”
Bok skipper Siya Kolisi added: “We knew it was going to be a tough game. Hopefully we’ve done enough to qualify for the next round.”
One casualty for South Africa was a suspected fractured cheekbone for winger Makazole Mapimpi who was forced off after an unfortunate clash of heads with Augustine Pulu that referee Luke Pearce ruled did not merit a yellow card.
Tonga coach Toutai Kefu said he was proud of his team’s performance after disappointing opening losses to Ireland (59-16) and Scotland (45-17).
They will wrap up their campaign confident of a first victory of this World Cup against Romania in Lille on October 8.
“I would have preferred the result!” Kefu said when asked how pleased he was at seeing the team score three tries against the defending World Cup champions, South Africa having previously conceded three over nine matches.
“The boys had a real dig. One of the main things we stressed before the game was putting on a performance that everyone would be proud of and that was one of them.
“That is what rugby is all about. You want to play against the best. That’s what makes the good players get out of bed so it was a fantastic experience for everyone today.”
Australia still alive
Meanwhile, Australia coach Eddie Jones said on Saturday he was preparing his team for the quarter-finals following their 34-14 victory over Portugal that kept their faint Rugby World Cup progress hopes alive.
The Wallabies ran in five tries - three when Portugal had a man in the sin-bin - on their way to only their second victory of this tournament in France.
Defeats to Fiji and Wales - the latter by a record score - has left them knowing that progress is out of their hands.
If Fiji take any points against Portugal next weekend, Australia will be out.
“We’re still alive. That was the aim of the day,” said Jones, who praised his team’s resilience during a second-half period when they had two players in the sin-bin.
“For a young team down to 13 men we showed plenty of courage and fought hard.
“We’ve done that all season, sometimes the results haven’t been in our favour... well, most of the time.
“It’s a real credit to them. You look at the experience of our players out there, we’re averaging less than 20 caps.:
Australia now face a frustrating and uncertain week ahead, waiting for the final Pool C matches where their fate will be determined.
Fiji will be favourites to beat Portugal and join Wales in the quarter-finals but there is still a small chance of Australia going through if Portugal were to win and deny the Pacific Islanders a bonus point.
“I’ve never experienced this before so I really don’t know,” Jones said when asked what he felt about the uncertainty ahead.
“We’re anticipating we’ll be in the quarter-finals so we have plans to have three days off and then three days training,” he said.
“We’ll see on Sunday night. Portugal played with plenty of spirit tonight so you never know.”
And while many people expected Australia to win more comfortably than the final score, Jones insisted he was happy.
“I thought defensively we worked really hard. Attack-wise we had bits and pieces.
“We still lack that clinical edge to our game. We do some good things and then we give the ball back too quickly.”
After the game, the Wallaby players came together in a circle and captain David Porecki said the mood was positive, despite their likely looming exit.
“It was celebratory. I’m proud of the boys, it was a tough week to turn it around and we did that,” he said.
“It wasn’t sombre at all, it was positive.”
‘Imperfect, giving, exciting’
Portugal’s French coach Patrice Lagisquet said he had some regrets after his side scored the opening try through Pedro Bettencourt but then saw the centre sin-binned soon afterwards and conceded three tries while a man down.
That took the game away from them with two thirds of it still to play.
“There’s a mix of frustration and pride. Frustration because at 15 against 15 we would maybe have resisted better,” he said.
“The yellow card hurt us badly, we weren’t able to manage that period.
“We should have kicked differently, not systematically in an attacking way as we did but to send them back into their half.”
But he praised his side’s style of pay, which had the crowd of more than 40,000 people in Saint Etienne regularly on their feet.
“With a bit more experience this team could be a bit more ambitious,” he said.
“But it’s a joy to coach this team. They are imperfect, they have shortcomings, but they are so giving, exciting, they play complete rugby.
“It’s great to coach them and I think the players enjoy it and the crowd too.”
Next up it will be Fiji but Lagisquet admitted he is not confident.
“I’m a little worried about our next match against Fiji. They didn’t manage their game against Georgia well and I’m afraid they will want to make up for it against us.”
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