Brook is under pressure to perform, here we break down the fight and explain why the Brit could come unstuck against Rabchenko.
But he drew a line under those twin defeats in emphatic style by ending the challenge of the rugged Rabchenko within five minutes to send a warning to the top tier of 154lb fighters.
"I've never been satisfied winning one world title".
Brook landed an early straight left hand down the middle and grew in confidence as the first round wore on before stepping things up in the second. If it's at welterweight, I would personally say Amir Khan.
"I felt strong at the heavier weight".
"I've had six months off so there was no way I was going to box at 147 anyway but I think that 154 is really going to suit me".
"I just felt a lot healthier and when you're getting older (trying to lose weight) takes it out of your legs and body, it's like taking weight off a stone, there's nothing to take off me". "We've got the same promoter, so why can't it happen?"
Brook kisses his partner Lindsey Myers in the ring while holding his new belt after his win
"I'm the terminator and I'm back".
The fate of Sheffield's Westgarth - who died on Sunday just hours after falling ill following a fight that he won at the Doncaster Dome last Saturday evening - will not be far from the thoughts of Brook, his corner and numerous fans inside the FlyDSA Arena tonight. He's a respected champion and I destroyed him in two round easily. I stand at 6ft tall, walk around 171-172lbs lean, make 154lbs very easy and I have no need to move up.
The fight is a fascinating encounter, not only because it should be competitive, but because Brook is fighting to silence his doubters, prove his fitness and spark an assault on becoming a two-weight world champion. I don't know how the bookmakers made him favorite.
Florida-based Thomas, 32, has revived his career after a third-round knockout defeat to Russia's Andrey Fedosov in ESPN's 2015 Boxcino Tournament, but this was a frustrating night for him as well as Allen. Galahad is the IBF No. 5, with just Joseph Diaz Jr. and Carl Frampton ahead of him in the rankings other than champion Selby and Warrington.
After he was pulled out by his corner in the fifth round when he suffered a fractured eye socket, all thoughts turned towards his next fight, back at his natural weight class and at the stadium of his beloved Sheffield United.
"I want the victor out of Warrington and Selby, that's the one I want".