"The nerves are way worse [than on
Idol]," David Cook told reporters moments before his Tuesday night rendition of "The Star-Spangled Banner." "It's the one song you don't want to mess up. I'm going to try not to notice Jack Nicholson sitting in the front row and think about the lyrics."
The only saving grace about his performance before game three of the Celtics-Lakers NBA championship series?
"No matter what I do, I don't have Simon [Cowell] telling me how dreadful it was," the 25-year-old joked.
But the Idol winner nailed the vocally and lyrically tricky anthem – and was spotted backstage looking relieved.
"It was crazy," Cook told PEOPLE. "I still have the shakes a little bit. I got through it. I don't think I messed up any words."
His girlfriend, Idol alum Kimberly Caldwell, was there to cheer him on. But even with her support, Cook said, "That was the scariest thing I have ever done."