The 38-year-old kicked off the first leg of her residency, dubbed "The Xperience", at Zappos Theater in Planet Hollywood on Friday, May 31.
When asked by reporters from Extra TV how it felt to have the support of the 26-year-old, the "Beautiful" hitmaker replied, "Amazing. It was so wonderful to have her support, her love and energy at the show. She's a blessing."
The "Skyscraper" singer documented the show's opening night on her Instagram Stories, and praised the star as being absolutely "perfect."
"The f**king queen herself," Demi captioned a series of snaps of the duo backstage.
"A PERFECT, perfect show.. Couldn't believe it was opening night because it was so smooth, flawless and sounded incredible," she continued. "I was entertained the entire time and was so bummed when it was over until I was reunited with this beauty. I'm so so happy I got to hug you @xtina."
The pair have a well-documented friendship, having collaborated on Christina's 2018 hit "Fall in Line", and the star supported Demi as she celebrated six months of sobriety last December (18).
Commenting on a photo of the "Camp Rock" star looking happy and healthy following a workout, the pop icon told her friend she had missed her "so very much."
"And we keep on tickin' - till the end of time- I looooove youuuu," Christina added.