Soccer's shining moment continues to be overshadowed by violent protests across Brazil.
Sunday night in Rio de Janeiro, a police officer fired what appeared to be a live round into a crowd of demonstrators, reports CBS News' Elaine Quijano.
Earlier, another group of protesters threw Molotov cocktails. Police responded with tear gas and percussion grenades, hoping to disperse the crowd outside Rio's famous Maracana stadium.
Team USA arrived in Natal with their game faces on.
"We know it won´t be easy but certainly we feel like if we step on the field and are sharp and play to the best of our ability we can have a really good World Cup," midfielder Michael Bradley said.
Their coach, Jurgen Klinsmann, who's been criticized for his lack of optimism, struck a more positive tone Sunday.
"Hopefully we can deliver some goals tomorrow well and we can have at least one goal more than Ghana," he said.
American fans who traveled to Natal see this tournament as a chance to prove U.S. soccer can compete with the world's best.
"Before we were coming up as a soccer team a soccer nation, but now we have the players, we have arrived. And we are here to seek revenge tomorrow," a fan said.
Grant Wahl, senior writer with Sports Illustrated, is following the team through the tournament.
"The U.S. has advanced now as a soccer nation to the point where, no matter who your World Cup group opponents are, the expectation should be to advance from the group," he said.