The 58-year-old television personality and 34-year-old singer dressed and performed as the "Chandelier" songstress on The Ellen DeGeneres Show and Facebook Live, respectively.
DeGeneres wore a poufy dress and black and white wig as Sia on Monday's episode of Ellen. She was joined by model Heidi Klum, who went as dancer Maddie Ziegler, a frequent collaborator of the singer's.
"Happy Halloween, everybody!" DeGeneres said. "As you can tell, I'm Sia, and the problem is I can't really see ya. I made this costume myself. I found some old loofahs backstage. It was not that hard to make. And then the bow is from a car I gave away recently."
"Sia and I have a whole lot in common. She's Australian, and I married an Australian, and we both like to swing from a chandelier -- which is why I'm no longer welcome at Bed Bath & Beyond," she joked.
Clarkson had worn a similar outfit to channel Sia in her Facebook Live post Friday. The "Piece to Piece" singer hosted a masquerade ball for Halloween the next day in Nashville, Tenn.
"Welcome, hey, what's up? I'm Sia this Halloween. She's one of my favorites, so I thought I'd wear a wig and be Sia," she said.
"I don't know how she does this 'cause, you know, you can't see. But it's also kinda awesome 'cause you're in your own little world when you're performing. I love that song. Everybody loves that song," the star added after her cover of "Chandelier."
Sia herself seemed flattered by the attention, encouraging fans to show off their Sia costumes with the hashtag "#itsasiahalloween." The singer last released the album This is Acting in January, which debuted at No. 4 on the Billboard 200.