Kelly Clarkson can certainly evoke emotions with her singing. But the first winner of “American Idol” performed a song so powerfully Thursday night on the Fox TV show that it brought not only the audience but even herself to tears.

Of course, as she noted, being seven months pregnant and overly sensitive didn’t help.

Clarkson had returned to her old stomping grounds to serve as a guest judge as part of the final season of “American Idol” and to perform her new song, “Piece by Piece.” Viewers and the audience got a tipoff of what was to come when host Ryan Seacrest referred to it as “a very emotional song” in his introduction.

Then Clarkson began singing about being abandoned by her father at 6 years old:

And all I remember is your back
Walking towards the airport
Leaving us all in your past

As the song, which Clarkson co-wrote, continued, she sang of finding the man who would become the father of her two children:

He never walks away
He never asks for money

He takes care of me

He loves me

Piece by piece

He restored my faith

That a man can be kind
And a father could stay

That’s when the audience started to lose it.

Tears visibly started flowing from several of the contestants watching from the stage, as well as celebrity judges Keith Urban and Jennifer Lopez. Country singer Urban, in particular, became more and more affected as the song went on — as did Clarkson.

She paused a few times and had to restart some lines. After she struggled to sing the last few words, the audience leaped to their feet with applause, rhythmically shouting, “Kelly! Kelly! Kelly! Kelly!”

When host Ryan Seacrest bounded to the stage to chat, Clarkson apologized for breaking down.

“I’m pregnant, and it’s nostalgic, and I can’t believe it’s the last season,” she explained. “Yeah, really sorry that I just bawled.”

She added, with a laugh, “I’m actually quite proud that I made it that far!”

Urban later tweeted to Clarkson: “I am truly speechless. Thank you for gracing us tonight with your beautiful heart, soul, gift, & your pure humanity!”

On Friday morning, "Piece by Piece" was the No. 1 download on iTunes.

Clarkson won the first season of “American Idol” in 2002 and has gone on to score hits such as “Since U Been Gone” and “Miss Independent,” and has won many awards, including three Grammys.

Check out the video of her performance of “Piece by Piece” above.