The 42-year-old was up against Emma Sophina and Kimberley Bowden for a moving 'Survivors'-themed sing-off.
Emma survived the Hudson River plane crash; Kimberley tragically lost her father two years ago; and Natasha has finished 20 weeks of gruelling chemotherapy after being diagnosed with breast cancer last year.
The trios coach Delta Goodrem was so moved by their performance that she joined them on stage for the Knockout.
Goodrem later took to Twitter to thank the the trio for allowing her to share the touching moment with them.
"Wow, to be able to share this moment with these three women. I can't even begin to describe it," she wrote.
Goodrem herself was diagnosed with Hodgkin's lymphoma at the age of 18.
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