At a joint press conference with Motlanthe, FIFA president Sepp Blatter attacked sceptics who doubted South Africa could organise the tournament but said sometimes he had needed to push authorities to ensure everything would be ready on time.
"From time to time we had to put on some pressure but I never had any doubt. Now it's time for the world of football to accept the tournament will go ahead in South Africa," he said as the 100-day countdown began to the World Cup.
"We have come a long way to where we stand now only 100 days from kick-off. It has been a long road paved with trust and confidence but with patience as well," Blatter said, repeating a well-worn theme of several months.
"There was a lot to do to change mentalities and to convince people, even within FIFA," he said of the decision to allow only African countries to bid for the hosting of the 2010 finals, adding, "a dream is now a reality".
Motlanthe said the World Cup had brought major economic benefits to South Africa.
"We invested billions in infrastructure ahead of the world recession and those benefits have been already felt by all South Africans. The hosting of the World Cup will give an important impact to tourism. The country stands to benefit greatly from it," he said.
PROFITEERING WARNING
But he warned against profiteering, after complaints that hotels, airlines and other tourist operators were trying to make excessive profits.
South Africa has launched an inquiry into possible price-fixing by domestic airlines and officials have expressed concern about huge price increases by hotels, especially those outside the official grading structure.
"There will be no ripping off of any of the passengers by artificially increasing the airline ticket prices," Motlanthe said, although substantial increases have already taken place.
South Africa's airports are 90 percent ready to handle 120,000 extra flights - double the normal capacity - during the World Cup, the company running them said on Tuesday.
Airports Company South Africa (ACSA) said preparations would be complete by June after a 17 billion rand ($2.22 billion), programme of updates and expansion.
"With exactly 100 days to go, we are confident that... we will be ready to meet the requirements of this major event," said Chris Hlekane, General Manager of Johannesburg's O.R Tambo International Airport, which will be the World Cup hub.
South Africa has invested billions of dollars getting ready for the continent's first World Cup, but hopes to recoup that and more through investment and tourism in the years to come.
The countdown to the last months of preparation switches focus on Wednesday when South Africa's under-performing national side take on neighbours Namibia in a warm-up friendly.
