"It will be a wonderful World Cup. Trust South Africa," Blatter told reporters at FIFA headquarters on Thursday.
"It's to reward a continent which has given so much to the whole world. Football has taken a lot out of this continent and it is time to give something back.
"A lot of politicians have congratulated us for going there.
"Yet we go to Africa and a question mark appears. Two weeks ago, we had an ATP tennis tournament in Johannesburg and nobody said anything."
FIFA general secretary Jerome Valcke likened the tournament to a car.
"We have a very good car, a very strong car. We have filled the tank with petrol and can run the car for 40 days," he said.
"We are adding oil to make sure everything will keep working. We have the four wheels but we are still missing a few things."
He said the major hitch was that the Soccer City stadium in Johannesburg would only be finished on March 15.
"We are more or less on track, less with Soccer City where we have not yet received the stadium.
"It is not fine not to have one main stadium ready now. We are not able to run any tests events for the time being.
"All the other stadiums are fine. Durban is one of the most beautiful stadiums ever for a FIFA World Cup."
CRIME RATE
With airlines and hotels being criticised for hiking fares, Valcke said Emirates had recently reduced prices on some routes by a third and had agreed to open up new routes to South Africa.
The country's crime rate has also been one of the main concerns in the run-up to the finals but Valcke said any area connected with the World Cup - such as stadiums, hotels and airports - would get extra protection.
"The event itself will be secure," Valcke told reporters. "Nothing will happen within the World Cup zone."
However, he could not guarantee a legacy in terms of security.
"I am not sure South Africa will be safer after the World Cup, although they will have a large security system in place with cameras and control systems," he said.
"It's a very low level criminal system. It's a young democracy, there are a lot of guns around but the violence in (2014 World Cup host country) Brazil is more organised."
"On the other hand, I can tell you about some places in Paris where it's not safe and where I wouldn't go alone," added the Frenchman.
South Africa has one of the world's highest rates of violent crime, with 50 murders a day - more than the United States which has six times the population.
More than 40,000 police are being mobilised to protect the month-long World Cup tournament which starts on June 11.
