KSI took on professional boxer Luis Alcaraz Pineda in his second fight of the night at the O2 Arena.
'The Nightmare', who is on a mission to end Jake Paul's boxing journey, was initially scheduled to fight YouTuber Alex Wassabi until he had to pull out with injury.
Rapper Swarmz was drafted in as a late replacement but then it emerged that KSI would be taking the huge step of fighting two different opponents - one of which would be a boxer - on the same bill.
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Scheduled opponent Ivan Nikolov was taken off the card and replaced by Pineda after receiving backlash for racist tattoos.
But the challenge remained the same for KSI and he kicked off the card with a brutal second round knockout of Swarmz.
And after his younger brother Deji recorded his first ever win with a stunning performance against Fousey, KSI ensured it was a third win for the family in the main event.
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Displaying plenty of power in his strikes, he knocked down Pineda twice in the opening round and the Mexican was constantly complaining about what he felt was illegal shots.
He repeated his efforts in the second and even performed press-ups while the referee did his count.
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Somehow, despite taking a lot of punishment and barely throwing anything back, Pineda made it to the third and final round, where he was finally put out of his misery.
KSI, who was out of the years for three, moved to 3-0 professionally and after becoming the new IBC cruiserweight champion, called out YouTuber Slim, Andrew Tate and Tommy Fury amongst others.
Josh Lawless