Clarkson (left) admits she is a fan of Taylor's
US singer Kelly Clarkson has hit back at Taylor Swift's management, who defended the star's off-key performance at the Grammys on Sunday.
Scott Borchetta, of Big Machine Records said: "This is not American Idol."
He added: "This is not a competition of getting up and seeing who can sing the highest note."
Writing in her blog, Clarkson - who won American Idol in 2002, said: "We not only hit the high notes, we generally hit the right notes."
Mr Borchetta spoke out after mounting criticism over Swift's duet with Stevie Nicks at Sunday's musical awards show.
"This is not a competition of getting up and seeing who can sing the highest note. This is about a true artist and writer and communicator. It's not about that technically perfect performance," he said.
"She is the voice of this generation. She speaks directly to and they speak directly back to her."
He blamed the star's bad performance on a technical issue, and added: "It's that classic thing that critics do of building something up and then wanting to tear it down."
But Clarkson, 27, took exception to his comments in an open letter on her website.
"I understand defending your artist obviously because I have done the same in the past for artists I like, including Taylor, so you might see why it's upsetting to read you attacking American Idol for producing simply vocalists that hit 'the high notes'.
"Every artist has a bad performance or two and that is understandable, but throwing blame will not make the situation at hand any better.
"I have been criticised left and right for having shaky performances before (and they were shaky) and what my manager or label executives say to me and the public is 'I'll kick butt next time' or 'every performance isn't going to be perfect'.
"I bring this up because you should take a lesson from these people and instead of lashing out at other artists (that in your 'humble' opinion lack true artistry), you should simply take a breath and realise that sometimes things won't go according to plan or work out and that's okay."
Signing off, Clarkson said: "Sincerely, one of those contestants from American Idol who only made it because of her high notes."
In January last year, Clarkson made the largest ever leap to number one in US chart history, rising 96 places.
Her single, My Life Would Suck Without You, rose from 97 to the top of the Billboard chart after selling 280,000 downloads in its first week of release.