Jessie J may be a full-fledged pop star in her native Britain, but the songstress (and co-writer of hits including "Party in the U.S.A.") was still emerging stateside -- until she brought down the house with her killer performance on "Saturday Night Live" yesterday (Mar. 12).

The singer kicked things off right, with an assist from "Price Tag" collaborator B.o.B during the single's "SNL" debut.

Video: Jessie J & B.o.B, "Price Tag," "SNL," 3/12/2011

It was definitely a no lip-synch zone, as Jessie J freestyled her impressive, soulful vocals toward the end of "Price Tag" and all over her next sexy number, "Mamma Knows Best."

Video: Jessie J, "Mamma Knows Best," "SNL," 3/12/2011

Consider the energetic showing your initiation, Ms. J -- we're wowed.

Jessie J's debut album, "Who You Are," will see a U.S. release on April 12.