Demi Lovato surfaced in Vegas Friday night for a performance that brought her to tears.

Demi’s a superfan of one Christina Aguilera, who was performing at Planet Hollywood where she kicked off her residency.

Lovato scored second-row seats with her friends and she sang and danced during Christina’s opening night.

Check out the vid that Demi shot … snippets from “Genie in a Bottle,” “Ain’t No Other Man,” and “Fighter.”

Christina Aguilera is worthy of superfandom — she has five Grammys and has sold more than 75 million records.

By the way … Demi seemed great — she was happy, relaxed and genuinely excited.

Her residency at the hotel’s Zappos Theater — “Christina Aguilera: The Xperience” — runs through October, with some breaks in the middle.