May 23, 2011 12:28 GMT  ·  By

When Enrique Iglesias bailed out as opening act on Britney Spears’ upcoming tour, it didn’t take her long to find a replacement. Nicki Minaj and Britney got up on the same stage and performed together at last night’s Billboard Music Awards 2011.

The so-called “duet” kicked off with a lively, colorful and very energetic take on “Superbass” by Nicki, accompanied by dancers in wigs and outfits similar to hers, which made it look as if she’d just used cloning for her own show.

There’s no mistaking Nicki though, even if she wasn’t so set on turning her back to the audience to show which one is the real Nicki.

Towards the end of the performance, Nicki started namedropping Britney, which was enough of a cue for fans to understand that she would be coming up soon.

That, she did, as the video embedded at the end of this article will confirm.

Lights turned on on the side of the stage to show Britney in a tight little black dress and leather jacket with yellow stripes.

She started singing – lip-synching to – “Till the World Ends,” her most recent single from the album “Femme Fatale,” walked through to the front of the stage followed by Nicki and her dancers, stopped and posed. End of the song.

Though Britney rarely sings live, several loud voices in the blogosphere point out that she should have at least made an effort at the Billboard Awards, especially since she walked on the same stage as two other performers who did sing live: Nicki and Rihanna.

HitFix, for instance, rates Britney’s appearances as two of the worst moments of the night because they prove that she’s still a long way to being the Britney her fans fell in love with: the first has gone out of her.

“The pop princess’ set prior to ‘Femme Fatale,’ ‘Circus,’ may have marked a comeback, but that doesn’t mean Spears is in the fighting shape she used to be,” the e-zine says.

“Despite the joy of her unanounced visit, her piped-in, lip-synced vocals made her look foolish next to awards show collaborator Rihanna and future tour mate Nicki Minaj, and her moves continue to look stilted,” HitFix adds.

“And that robotic 1,000-yard stare rivals the creepy quotient of the latter’s patented Crazy Eyes. Wherefore art thou, Brit-Brit?” the e-zine asks.

Check out the performance with Nicki Minaj to see whether there’s any substance to these claims.