Monster hit! Lady Gaga’s Las Vegas residency is giving Gwen Stefani some stiff competition.

A new Vegas star is born! Lady Gaga’s Enigma residency debuted at MGM’S Park Theater on Dec. 28 — drawing famous fans including Katy Perry, Orlando Bloom and Celine Dion — and a source says it blows Gwen Stefani’s show out of the water. “Gwen’s facing some tough competition,” the source tells In Touch, noting that the 32-year-old “Born This Way” singer’s New Year’s Eve show was basically sold out, while Gwen, 49, still had plenty of empty seats. “She’s relieved most of her scheduled 2019 performances don’t fall on the same dates as Gaga’s!”