Victory or a draw for the Springboks would confirm a probable quarter-final appointment with Australia in Wellington on Sunday week.
But if Samoa tear up the form book - and Wales beat Fiji on Sunday - there is a possibility South Africa could make a pool stage exit.
The Springboks, though, remain firmly in control of their destiny, having emerged as probably the team most likely to prevent red-hot favourites New Zealand from marching towards a first world title since 1987.
"It is pretty tough playing against Samoa," said Habana, South Africa's record Test match try-scorer.
"That first 20 minutes (against Samoa in the 2007 World Cup) was some of the toughest Test match rugby I have ever played. It is tough, and tomorrow will be no different.
"Injuries are part of the game, and if you worry about it you are playing the wrong sport. Rugby is not a contact sport, but a collision sport, and you brace yourself for that.
"It will be a tough one."
After their narrow scrape against Wales, South Africa eased past Fiji and Namibia, scoring 136 points in the process and conceding just three as they established themselves as clear Pool D leaders.
"It has been a steady build-up for us," Habana added. "I think the games against Fiji and Namibia were good when we got into our structure. We showed what we can do.
"There were still a couple of negatives where a lot of individual turnovers and errors took us out of our structure, so we have to look at specific things. But three wins out of three World Cup games was what we were looking for.
"Within the team, we believe we can win the World Cup. The outside sources are not that important to us, and we put pressure on ourselves as a team and as individuals to perform.
"There will always be favourites, and the All Blacks have laid down the mark in the last couple of weeks.
"Tomorrow is a knockout game for us, and if we end up losing we might not even be in the quarter-finals. We can't focus on the big goal and that is to win the World Cup. We can only focus on Samoa."
Samoa, having beaten Australia earlier this year, are capable of giving the Springboks a serious examination, and their former London Irish centre Seilala Mapusua has rallied them for one last big effort in the pool stage.
"I think it (fatigue) is always a factor when it comes to the World Cup," he said.
"When you play in the World Cup, your body will take a lot of battering. That's why you have 30-man squads.
"But the boys have recovered well, and all we can do is ask for another great effort."
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