LOS ANGELES -- Florence and the Machine have performed at award shows in the past, but they've mostly been back at home in the U.K., and they've definitely never been as eye-catching, ambitious and downright exuberant as her upcoming performance at Sunday's MTV Video Music Awards. It's a matter of necessity.

After all, around the rest of the world, Florence Welch is a very big deal, a critical and commercial darling with an armload of hits and a devoted fanbase. But here in the U.S., she's just starting to break through, thanks in no small part to "Dog Days Are Over," a triumphant tune that's recently become the soundtrack to many a TV show and commercial (most recently, it appeared in trailers for Julia Roberts' "Eat Pray Love").

So her VMA performance is clearly a big deal, another (rather large) steppingstone on her way to Stateside success. And, somewhat accordingly, everyone involved with the show is aiming high.

"People have heard the song on television, but maybe those people haven't made the connection to Florence the artist, so that's part of what her performance is going to be about," Dave Sirulnick, VMA executive producer, told MTV News. "It's going to be beautiful, breathtakingly done and otherworldly. And maybe it will help launch her here in the States. We want viewers to watch it and say, 'That was spectacular.' "

Judging from what we saw in rehearsals Friday (September 9), that may very well be the reaction. Part classic revue, part joyous sing-along, part kinetic, hippie-esque freakout, it's a strangely perfect summation of Welch herself, not to mention a rather fitting tribute to her VMA-nominated "Dog Days" clip. There may not have been any explosions (or floral arrangements) -- like Welch promised when we spoke to her Thursday -- it hardly mattered. This is definitely going to be a big performance, one people are going to be talking about. And yes, they'll probably be saying, "That was spectacular."

The 27th annual MTV Video Music Awards will be broadcast live from the Nokia Theatre in Los Angeles on Sunday. The party starts with MTV News' VMA Pre-Show at 8 p.m., followed by the main event at 9 p.m. ET/PT.