Kelly Clarkson has written an open letter to a record executive who defended Taylor Swift's off-key performance at the 2010 Grammy Awards by declaring, "This is not American Idol."

Big Machine label boss Scott Borchetta came to Swift's aid on Thursday after critics picked apart her duet with Stevie Nicks at the Los Angeles ceremony last week.

Borchetta said Swift should be excused for the slip and cited the hit TV talent show in his defence of the singer.

He said, "This is not American Idol. 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."

Clarkson, who shot to fame after winning the first season of American Idol in 2002, has blasted Borchetta in an open letter after taking exception to his comments.

In a post on her official blog, she writes, "Wow... Dear Scott Borchetta, 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'...

"You know what, we not only hit the high notes, you forgot to mention we generally hit the 'right' notes as well. 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."

The pop star then signed her message, "Sincerely, One of those contestants from American Idol who only made it because of her high notes."