On Saturday, Mayer, who happens to be Down Under to promote his own album, Tweeted the following: "If you're shocked that Britney was lip-syncing at her concert and want your money back, life may continue to be hard for you."
Why all the fuss?
On Friday, about 100 angry fans reportedly stormed out of Britney's concert at the Burswood Dome in the Western Australia city of Perth, saying they were disappointed by the lackluster performance and Spears's lip-synching during her two-hour show. Spears gave Perth fans a generic welcome, never mentioning their city by name. "What's up Australia?," she said from the stage. "How you feeling tonight? It's so good to be here tonight. Your country is beautiful."
One disgruntled concert-goer, Wendy Di Renzo, 36, said she paid $148 for her ticket. "It was so impersonal. She did not interact with her audience," she says. "There were no big TV screens projecting the action, so if you didn't know Britney, you might have even doubted it was her."
Meanwhile, politicians in three Australian states – Western Australia, Victoria and New South Wales – have called for new laws to force music promoters to disclose whether a concert will be live or lip-synched.
Yet Britney clearly left many of her fans satisfied. They have flooded her Web site with messages of support, and praised her for putting on a good show. "I paid $AUS 1,500 [nearly 1400 U.S. dollars]," wrote one. "To see a fantastic artist perform and sing in front of me is my dream come true. I love you Britney."
Another fan, Scott Bown, 16, tells PEOPLE the concert was "great" and Britney was "amazing." "People should stop being nasty about her and get a life," he says.
Spears, who is traveling with her father, will perform in Melbourne on Nov. 11.
Reporting by PERNILLA CEDENHEIM