The original Idol winner sang the emotional song "Piece By Piece" onThursday night, the lyrics at times prompting her to pull away from the mic to regain composure.
The tune, written about an absent father, included lines such as, "I begged you to want me but you didn't want to," and, "Piece by piece he restored my faith that a man can be kind, that a father could stay."
Judge Keith Urban was visibly moved by the song as he stood to applaud her at the end of the performance, tears in his eyes.
"Super pregnant and hormonal," Clarkson explained about her raw stage presence. "I'm pregnant, and it's nostalgic, and I can't believe it's the last season. I'm really sorry I just bawled."
The soon-to-be mother of two said she wrote the heartstring-tugging tune while she was pregnant with her first child, River Rose, with husband Brandon Blackstock.
Last November, Clarkson released a heartwarming music video for the song. It features then-17-month-old River Rose. On Facebook, the singer explained the song was the "happy ending to 'Because Of You.""