The World Cup, though, may have changed that.

Fans -- both new ones and diehards -- energized

You could see the support at Chicago's Soldier Field, where thousands, some of whom admitted that they'd played hooky from work, gathered to watch the game.

The lakefront stadium is better known as home to the other game of football -- the NFL and its Chicago Bears -- but on Tuesday, its gates were opened to the public. Thousands of fans sat in the stands or stood on the gridiron, which was covered with a protective matting.

"National Watch Soccer Day," one fan said.

Similar scenes played out in AT&T Stadium, home to the Dallas Cowboys of American football lore.

Freedom Plaza in Washington was also packed with American fans. So was the South Court Auditorium of the Eisenhower Executive Office Building, where the attendees included President Barack Obama, who even started a cheer of "I believe that we will win!"

Rival sports leagues and stars, like the NFL, also offered their support.

Major League Baseball tweeted out pictures of Phillies, Astros and Twins players watching the U.S.-Belgium game. The Red Sox's Johnny Gomes rocked a tank top and shorts that doubled as American flags while taking batting practice.

Los Angeles Laker Kobe Bryant tweeted his congratulations on Twitter, saying, "Well done #USMNT mde our country proud. #USsoccerOntheRISE #WorldBWarned."

Bryant has made his love for "football" known for some time. But what got many in the U.S. soccer world so excited this summer was all those who usually don't care about the sport following the game -- like one man who posted to CNN.com's match blog, "I hate soccer and yet here I find myself hanging on every post about the game."

A patron at Nevada Smiths sports bar in New York, John Paul Ovadia, remarked how soccer was once a marginalized sport in the United States, but not any more.

"I think every four years there's more and more interest," Ovadia said. "And the further the U.S. goes, the more people are paying attention."