Campanella was representing California when she won the Miss USA 2011 pageant at the Planet Hollywood Resort & Casino in Las Vegas on Sunday.
Speaking on NBC's Today this morning, she said: "They list the runner-up first and of course you don't want your name called at that point. When Giuliana Rancic said, 'The Miss USA 2011 is Ca...' I knew... My jaw dropped to the floor."
Campanella, from Sherman Oaks, triumphed over Miss Tennessee Ashley Durham in the final. Before the result was revealed, co-host Andy Cohen told the audience that Campanella and Durham were close friends.
"We were actually hoping it would come down to us two because we'd be happy either way it went," said Campanella. "So when it came down to us two we were so excited."
Campanella, 21, will now represent the USA at the Miss Universe pageant in Sao Paulo, Brazil on September 12.
Watch more of Alyssa Campanella's appearance on Today: