Jurgen Klinsmann's side impressed during their pre-tournament friendlies, beating Azerbaijan, Turkey and Nigeria.
But despite their strong form, captain Dempsey is not taking anything for granted ahead of a tough Group G campaign, which sees them face Ghana next Monday before then taking on Germany and Portugal.
"We were able to get three wins (in their friendlies) but it's different when you come to the World Cup and play these games," he said.
"We have got to be ready and I think we will be. It is great to be captain of this team.
"We have a good mix of young kids and guys with experience; we're excited about the team we have.
"We have attacking players who are contributing goals and we're coming off three wins."