The Girls Aloud star was on before show headliners 1D at the massive O2 Arena - and will return to the venue to headline the second night of the annual shindig with her band this evening.
Last night's show was opened by boy band JLS, who were followed by Little Mix (minus a poorly Perrie Edwards), The Script, Little Mix, Rizzle Kicks and Lawson.
Chezza was up next - performing a selection of her tracks including Fight For This Love and closing her performance with a surprise guest appearance from Will.I.Am for 3 Words.
One Direction hit the stage next - getting a wild reception for hits including What Makes You Beautiful and Live While We're Young.
And it was left to US star Bruno Mars to close the show, finishing on a cover of Valerie.
Tonight's show will feature Girls Aloud, The Wanted, Calvin Harris, Example, Rita Ora, Conor Maynard and Pink.
We told you yesterday how Chezza is apparently taking legal action over her former job on The X Factor USA.
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