Namibia captain Jacques Burger fears his team will be made to pay by South Africa in Auckland on Thursday night if they do not reduce their error count.
The Springboks are strong favourites to claim a third successive Pool D victory and maintain the heat on group rivals Wales, Samoa and Fiji.
Namibia, meanwhile, have already conceded 98 points in losing their opening two games against Fiji and Samoa, while they will have just a four-day turnaround before tackling Wales in New Plymouth next Monday.
Saracens star Burger, though, has no doubt his team will relish a chance of facing the reigning world champions - a side his countrymen have a lot of time for.
"It is partly like playing your brother," he said. "We are excited.
"We made a few mistakes in our other two games, and that is how we learn. We have to make less mistakes. Good sides make you pay when you make mistakes.
"When we get the ball, it is precious, and we have to keep it. Mistakes are points, so we have to cut them out.
"A lot of people in South Africa have a soft spot for Namibia and they will get behind us. You have that support every day and you can feel the support from the people.
"I definitely think we will do well - let's start the game and get going."
Wing Bryan Habana returns to the Springboks side after missing their victory over Fiji, while there are also starts for the likes of scrum-half Francois Hougaard, prop CJ van der Linde and flanker Willem Alberts.
South Africa assistant coach Gary Gold said: "It is very dangerous ground if you think that any opposition is potentially weaker than another.
"If you go in with that mindset, you can be in for a bit of a rude awakening.
"Rugby is in their (the Namibians') blood as much as it's in our blood. They are going to want to come out and prove a point."