Johannesburg - FIFA is investigating why a section of seats in the Soccer City stadium was unoccupied during the World Cup opening match between South Africa and Mexico.
"There was one block that looked empty and our people in ticketing are looking into it," FIFA spokesperson Nicolas Maingot said on Saturday.
The upper tier section of around 200 seats was filled by tournament volunteers later in Friday's match, which ended 1-1.
FIFA said 84 490 people attended at Soccer City - a record for one of its matches in Africa.
All tickets have been sold for Saturday's matches between England and the United States at the 45 000-capacity Royal Bafokeng stadium in Rustenburg, and at 62 500-capacity Ellis Park in Johannesburg where Argentina face Nigeria, FIFA said.
Around 3 000 tickets were still available early Saturday to see South Korea face Greece at the 46 000-capacity Nelson Mandela Bay stadium in Port Elizabeth.