Jesse McCartney forgets national anthem... in front of massive sports crowd

Pretty pop boy Jesse McCartney screwed up big time when he sang the American national anthem in front of a packed out racing crowd in California... and forgot the words.

Performing for the Pepsi 500 Nascar race in Fontana, Jesse fluffed a line of 'The Star-Spangled Banner'.

He did a pretty good job of covering it up - only to us Aussies who don't know the words! How embarrassing.

"Here at the Nascar race! So much fun! Can’t believe I forgot the words to the Anthem!" he Twittered after the slip-up.

"I’ve performed it 100 times. Bad nerves today I guess."

He joins a list of star performers who have also botched the lyrics during big events - including Macy Gray, Anastacia and funnylady Roseanne Barr.