The tour is her first since her 2009 Circus shows, which were marred by criticism of her decision to concentrate on her dancing instead of her singing by miming along to all of her hits.

But critics have heaped praise Spears following the launch of her new concerts, with a reviewer for Rolling Stone magazine revealing the singer is "progressing" her act. The review reads, "The night belonged to Britney: She managed to prove that she's still progressing as a showgirl... Not only that, she's doing it better than even die hard defenders would've predicted. At 29, the pop star whose career seemed in danger of ending just a couple years ago has shown that she's back - hopefully this time to stay."

Local newspaper The Sacramento Bee reported that her "performance truly began to sparkle," while celebrity blogger Perez Hilton applauded the singer for moving away from lip-syncing.

He writes, "Britney sings maybe 40 per cent of the show, which is really awesome considering that at the last tour she lip-synced every single song. I feel like this time the show and her are on the same level. Britney seems to have gotten her spark back."