(Reuters) -The World Cup "fever" sweeping the United States has surprised even soccer's governing body which is celebrating record viewing numbers in one of the markets it has long tried to crack, FIFA secretary general Jerome Valcke said on Friday.

"TV ratings in different countries are far higher than in 2010, not just in the normal football countries but also the USA where we reached a level which is just unique," Valcke told reporters.

"The fever of the World Cup in the U.S. is just amazing."

More than 18.2 million U.S. viewers watched the United States draw 2-2 with Portugal on Sunday, making it the most-viewed soccer match by an American audience.

FIFA said the viewing figures for that match were higher than for any of the NBA finals games and larger than the average television audience for the baseball World Series in 2013.

U.S. President Barack Obama was photographed watching Thursday's game between the U.S. and Germany on Air Force One and show business stars such as singers Rihanna and Justin Timberlake have been tweeting about the World Cup.

The U.S. lost 1-0 to Germany on Thursday but still qualified for the next round in which they face Belgium on Tuesday.

The United States staged the World Cup in 1994 and tried unsuccessfully to host the 2022 finals which were awarded to Qatar, but soccer has made huge inroads there in the last 20 years.

The United States are taking part in their seventh successive World Cup, a record currently bettered by only the major soccer playing nations of Brazil, Germany, Italy, Argentina, Spain and Asian heavyweights South Korea.

ONE OF THE BEST

Valcke told reporters the high-scoring football which has lit up the opening stages of the tournament has made this World Cup "one of the best ever."

"This World Cup will definitely remain one of the best ever when we are talking about the football played," he said.

"The level and the quality of football we have seen has been amazing and I am sure that it will be the same for the games coming up."

The 48 group-stage matches produced 136 goals at an average of 2.83 a game, higher than at any World Cup since the 1970 tournament in Mexico.

More than 2.5 million people watched matches inside the stadiums with more than 3 million fans seeing games in the so-called fan fests, where matches are relayed on giant screens.

Valcke, who famously told Brazil it "needed a kick up the backside" when he thought the preparations were flagging three years ago, could not resist making another point.

"The fan fests were sometimes questioned and became an issue in some of the cities," he said. "I mean, again, why have we been fighting to have the fan fests?"

A number of venues, most prominently Recife, queried the costs of providing the fan fests being staged.

"The fan fest is part of the World Cup. In Rio and the other cities it is just the perfect place to enjoy the World Cup if you don't have a ticket for the match," Valcke said.