Introducing the cover by stating it "definitely speaks to me", Selena delivered a pitch-perfect acoustic version of the track during a performance at a UNICEF charity concert with her band The Scene.
Ironically, Bieber performed the song back in November, when reports the couple had split first started swirling.
Gomez's cover featured a lyric switch, where she sang: "Boy I refuse, you must got me confused with some other girl," and she smirked as she sang, "the damage is done, so I guess I'll be leaving".
Looking all good-girl in a white shirt and matching flower headband, the singer giggled at the end of the track and said: "OK, that's enough of that."
During her UNICEF gig, Gomez also name checked her unlucky-in-love best pal Taylor Swift, and performed her current hit Trouble.