The Springboks just edged the first of eight matches over the weekend, which will decide the line-up for the knockout stage, prevailing 13-5 in a physical and sometimes fractious affair, which featured the first red card of the tournament.
A Bryan Habana try helped the South Africans put 13 points on the board in a dominant first half an hour but they were then forced to tackle for their lives as the Pacific islanders threw everything at them.
"We will never find a more physical game in the rest of tournament so we're happy to get through it," said South Africa coach Peter de Villiers.
The South African line was breached for only the second time in the tournament when number eight George Stowers inched over soon after the break but the Samoan assault was blunted when fullback Paul Williams was sent off 10 minutes from time for striking Heinrich Brussow in the face.
"Pretty disappointed, I'm proud of the boys, they gave it all they had," said Samoa skipper Mahonri Schwalger. "The ref was pretty hard on us, if a few calls had gone the other way, we could have scored more points against the South Africans." South Africa, seeking to become the first country to retain the Webb Ellis Trophy, finished top of Pool D and move on to a quarterfinal in Wellington, most likely against Tri-Nations champions Australia.
"We never came here to defend anything," De Villiers added. "We came here to compete. The team that won the cup four years ago may have a lot of the same names but it's not the same team." Samoa go home having failed to secure the bonus point that would have given them a chance of overhauling Wales, who now just need a single point against Fiji in Hamilton on Sunday to progress.
Wales coach Warren Gatland wants more than just progression, however, and on Friday he named the more attack-minded Rhys Priestland at flyhalf ahead of the steady Stephen Jones in his team to face the Fijians.
"We know if we can win one more game, and win it well, that will give us the best chance of reaching the quarterfinals of the rugby World Cup with significant momentum," he said.
The All Blacks on Friday named the team that they hope will keep up their momentum in their final Pool A match against Canada in Wellington on Sunday.
Having already secured top spot in the group, however, coach Graham Henry allowed himself a sentimental indulgence by moving the in-form Israel Dagg to the wing to allow fullback Mils Muliaina to win his 99th cap.
Scotland, who could still provide the hosts with their opponents next weekend, were looking anxiously at the weather forecast hoping the rain threatened for Auckland will bypass Eden Park during Saturday's Pool B showdown against England.
The Scots need to beat the 2003 champions by eight points or more, or run in four or more tries in victory, to have any hope of a place in the quarter-finals.
Australia still need a victory over Russia in Nelson on Saturday to be certain of their place in the quarterfinals but they will not be sure of their last-eight opponents until Ireland take on Italy in the Pool C finale on Sunday.
Ireland's stunning upset of Australia at Eden Park two weeks ago turned the group, not to mention the tournament draw, upside down and still clearly haunts the Wallabies.
"You don't want that to happen again," skipper James Horwill said on Friday. "It's a crappy feeling. We're going to do everything we can not to feel that way again." Ireland coach Declan Kidney sprung a surprise when he handed scrumhalf Conor Murray only his second international start in Sunday's "win or bust" game against Italy.
Despite that surprise, the Irish side for the encounter is anything but a reserve outfit, which vindicated Italy coach Nick Mallett's feeling about how his team has progressed.
"We've completely turned around the way other teams think about Italy. They used to be confident enough to put their B team in against us," said Mallett.
"No-one does that against Italy any more."
