Olly Murs and Joe McElderry will now sing again on Sunday night and face the last public vote.
Earlier in the show, Stacey sang a duet with Canadian singer Michael Buble. The pair sang Feeling Good, the song made famous by Nina Simone.
Stacey also tackled What a Wonderful World, which she sang for her first X Factor audition, and also performed on Tuesday at her old school, King Solomon High School in Barkingside.
Her final song was Queen's Who Wants to Live Forever, which won her the most praise from the judges, with Simon Cowell enthusing:"Stacey, you absolutely smashed it."