"Honestly, I was thinking, 'Please let it be Kelly Clarkson' and that surprises people," said Guarini.
He said the winner of "American Idol" sang the final songs better than he could, and it felt right.
"I was thinking, 'Man, there's going to be a national riot if she doesn't win.'" Guarini joked. "I mean, it was close, but those are her songs, and she did them so well."
He said America's choice to win was the logical one, and he's happy that one of his best friends was able to shine in the winner's limelight.
However, the runner-up position on the show isn't a bad place for Guarini. "American Idol" creator Simon Fuller rewarded the 6-foot-1-inch singer with a management contract. Fuller's 19 Entertainment already signed "American Idol" contestant Tamyra Gray and winner Clarkson. 19 Entertainment formed and managed the Spice Girls, S Club 7 and helped steer former Eurythmics singer Annie Lennox's solo career.
He says the experience of the competition taught him to be himself and true to his instinct. "I learned what works for me," said Guarini.
He also credited "mean" judge Simon Cowell to helping him grow as a singer. "He has definitely pushed me to be better," said Guarini. "He doesn't just say thing for ratings. He's got to be straightforward. He's working with the winner. He's working with Kelly, and he had to be satisfied."
Guarini desribes Cowell as a tough guy, but off the screen, he says, the Brit was wonderful and supportive. "He just got the whole Simon thing about him," said Guarini. "And he's a great guy."
Before Guarini became familiar to his television fans, he was just another struggling artist. The Doylestown, Pa., native put in two years at the University of the Arts, followed by two years at the School for Film and Television in New York. He didn't graduate and went back home in 2001 to join Cutting Edge Entertainment.
With his time at Cutting Edge, he performed at local weddings and the bar-mitzvah circuits.
"I guess I've been fortunate with the fact that I did get up in front of people to perform and to perform in front of kids – who are some of the toughest audience," remised Guarini of his humble singing career. "I got in front of high schools … in front of whatever and that really prepared me for what I'm doing."
One day in spring, Guarini's mom, Kathy, a former television reporter, was ironing when she saw a commercial for the "American Idol" auditions. She told Guarini about it. At the time, he had just started selling burglar alarms door-to-door.
"And a month later, I found myself, 5:30 in the morning, at Times Square in line and didn't get to audition until a quarter-to-two that day," said Guarini. "And then, I went to a couple of more auditions and went to the judges and the rest is history."
Guarini credits his mother for the position of opportunity he finds himself in now. And, perhaps inadvertently, he says, the competition helped save her health. Kathy was one of his strongest supporters, but she was unable to attend his final competition on "American Idol" because she underwent surgery to remove a tumor.
"If she hadn't come out there and supported me on the show, she would have never found out about the tumor," said Guarini. "She would have never known. She would have been walking around with a semi-cancerous lump inside of her. And it just been a blessing that she found out and had it taken care of."
Guarini will join the show's 30 finalists for a live performance in Las Vegas on Sept. 23 at the MGM Grand in Las Vegas. After that, the top 10 finalists will go on tour around the nation.