The bearded contestant received the least public votes and ended up in the bottom three on the reality talent contest, but was told by judges Jennifer Lopez and Randy Jackson that he deserved to stay.
Just as he was about to start singing 'I Don't Need No Doctor' in a bid to avoid the boot on the Fox show, Randy cut off the introduction so an amazed Casey could be informed there was no need for him to convince them of his talent.
Jennifer said: "We were wondering when we heard the results, 'Why is Casey at the bottom?' We don't know. You deserve to be here.
"We just want you to get back to the musician that you are. No more antics ... you deserve to be here."
Overcome with emotion, Casey said he couldn't believe it and fell to his knees.
He later said: "I thought that they ... I knew if there was someone that got cut tonight ... I thought they wouldn't use the save.
"It's unreal ... I started singing and the fact that you cut it ... scared the stuff out of me."
Stefano Langone and Thia Megia were also in the bottom three but no one was eliminated.