The Before He Cheats hitmaker and her fellow finalist Bo Bice were preparing for their last performance on the show, when Underwood was temporarily deafened during an ear piece fitting.
The pain was so severe, the 29 year old almost bowed out of the programme, but the determined singer pushed on and ultimately walked away as the winner of the fourth season in 2005.
During a Vh1 Tv special, Behind the Music, she recalled, "We were getting fitted for in-ear moulds, and I had an incident with the lady that was doing mine and she managed to hit my ear drum. I was like in ridiculous pain, and I couldn't hear out of one of my ears, like nothing. It was dead... So I just crossed my fingers, hoping I was singing on key."
The Grammy winner's mother Carole is proud her daughter pushed through: "Her ear was hurting her really bad, but the show must go on. And you can't whine and complain about it."