The contestants weren't the only ones singing on "The X Factor" last night -- so did Britney Spears  ... like, for real!

While the singer has a reputation for lip-synching her concerts and live appearances, on last night's episode of the FOX reality show she actually sang for the cameras.

Spears, 30, presented L.A. Reid with a cake and sang him a sultry version of "Happy Birthday" -- and we're pretty sure L.A. was as shocked to see Britney's performance as we were at home!

And she actually sounded pretty good.

Spears' performance was only one of a few good ones from last night's episode. Check out the other highlights below:

Panda Ross definitely won the evening.

The 42-year-old beat pneumonia just in time to perform to her "baby daddy" Simon Cowell ... or at least so thought she did. After her amazing performance of "Bring It On Home," she was rushed to the hospital ... but not before winning the hearts of the judges and the audience with her voice and big personality.

For the groups, we really liked Sister C ... a group of, you guessed it, sisters with some killer Dixie Chicks-like harmonies.

And we also had a soft spot for Jessica Espinosa, who performed a soulful version of P!nk's "Nobody Knows."

Are you rooting for anyone yet? Sound off below!

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