Fears of crime and high costs have sapped demand in several European countries, especially Germany, and organisers said a "significant number" of tickets had been returned, including by corporate sponsors.
They could not give details but said the fifth and final ticket phase would be launched on April 15, spearheaded for the first time by over-the-counter sales in South Africa via 11 new centres in the nine match cities.
"We want to make sure the picture we give to the world is full stadiums...that is why this phase is so important," said FIFA Secretary-General Jerome Valcke.
Valcke acknowledged that organisers had been slow to adjust to South African football culture where the mass of poor supporters do not have access to the Internet and are accustomed to buying tickets just before a game.
"The approach at the beginning was not the most friendly system for South Africa and South Africans. But there is always time to learn - 62 days (before the tournament) is a long period," Valcke said.
"We have always said that it is important that we make this World Cup more accessible to the (South African) people and with the over-the-counter sales, we believe this is a measure that is consistent with the needs of the fans," said chief local organiser Danny Jordaan.
Tickets are still available for all matches except the final and more than 100,000 of them will be available to South Africans for $20, the lowest World Cup price for many years.
USA TOPS DEMAND
Of the 2.2 million tickets sold so far, nearly 1 million went to South Africans. The United States, not a traditional football nation, surprisingly topped the foreign buyers with 118,945 tickets - way above third placed Britain with 67,654.
In Germany, where media reports of violent crime in South Africa have had a significant impact, only 32,269 tickets have been sold.
Valcke said American demand had been boosted by the work of the USA football federation to promote the game, and by the large number of Hispanic fans in the country.
Jordaan and other officials say costs to attend the long-haul World Cup have been a major factor in depressing foreign demand. The government has launched inquiries into both accommodation costs and alleged domestic airline price fixing.
Valcke said the sport's governing body was working with airlines and travel agents to get costs down. Fares from Japan have already been reduced.
FIFA is trying to encourage more than the existing trickle of fans from other African countries to attend the continent's first World Cup by organising special direct charter flights, Jordaan said.
Scheduled flights from the five other African qualifiers mostly take an expensive route via Europe to reach South Africa.
Valcke said the $20 match tickets may also be made available to neighbouring countries in another attempt to fill seats.
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