The 15-year-old wannabe singer, who suffers from Asperger's syndrome, went head-to-head with group Three Wishez and was eliminated from the reality television series.
Sykes performed Panic at the Disco's 'The Ballad of Mona Lisa', but was voted out by judges Ronan Keating and Natalie Bassingthwaighte. Guy Sebastian, as Sykes's mentor, obviously chose to save him.
Mel B opted to support Three Wishez, admitting that although she thought of Sykes as "endearing" and "quirky", she doubted that he could be "an international superstar".
During the live show, after performances from special guests Susan Boyle and Ricki-Lee Coulter, host Luke Jacobz also confirmed rumors that Kylie Minogue will be performing at The X Factor grand final.
There are now four acts remaining in The X Factor; Three Wishez, mentored by Keating, Sebastian's contestants Johnny Ruffo and Reece Mastin, plus Bassingthwaighte's protégé Andrew Wishart. Mel B has no singers left int he competition.
Sebastian was slammed by his fellow judges on Monday night for choosing the wrong song for show favourite Mastin.
Watch Declan Sykes perform below: