The Northern Irish singer impressed the panel and viewers alike with her rendition of Elton John's 'Your Song' during Saturday night's show.
The 16-year-old won strong praise from judges Gary Barlow, Tulisa Contostavlos, Kelly Rowland and Louis Walsh.
Devlin told The Sun: "I was kind of happy Simon wasn't there because I thought he'd hate me.
"Simon always just tells it straight, whether he likes it or not. But then I found out Gary was worse in terms of being honest, although, thankfully, he was good to me."
"Overwhelmed" Devlin said that the praise, which also came from celebrities on Twitter including Lily Allen and Rio Ferdinand, did "put more pressure on" her in the competition.
The X Factor continues on Saturday at 8pm on ITV1.
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> 'X Factor': 'Shy' Janet Devlin billed as new Diana Vickers after mesmeric audition - video
Watch Janet Devlin's X Factor audition below: