The Sheffield man chose to step up a weight division after suffering a shock defeat to Errol Spence Jr, which lost him his IBF welterweight title.
But the Belarusian was never able to get going against Brook, who will now have his sights set on challenging for world honours once more, or arranging a bout against his long-term rival Amir Khan.
Although both fighters' stars have faded since Brook won his welterweight crown, Khan and Pacquiao both remain lucrative possible match-ups.
Judgmental whispers about Brook's ring career have refused to die down, despite the fact the former world champion is looking for a fresh start against Rabchenko.
There was also the issue of Brook being blasted away by Spence Jr, the younger and much more sharp challenger. Rabchenko is 16/1 to stop Brook tonight, a method which would include Brook being pulled out due to injury.
Putting aside the potential weight issues, the biggest question hanging over Brook is the sturdiness of his eye sockets.
Those injuries are a major concerns considering Spence Jr targeted Brook's right eye last May, before breaking the left one. He has been a good fighter, but I'll have either of them at 154lbs.More news: Stephanie McMahon's Slap to Ronda Rousey Reportedly Legitimate
Yet Brook struggled to cement his own legacy as champion. Contests against elite champions like Golovkin and Shawn Porter will stand Brook in good stead against a man who has so far failed to make the leap.
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. However, despite the slight stagnation of Brook, his opponent this evening could be the ideal vessel for rejuvenation. Let's see how he gets on next month but here and now, it has to be Brook, for now.
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.
The first round was all Brook landing and boxing beautifully, after that he finished off his opponent in the second round rocking him and dropping him with a flurry of punches, the ref called the fight off as a hurt Rabchenko tried to get up to beat the ten count.
It was an easy night for Rabchenko, up against a 27-year-old who had a record of 4-20-2.
In stark comparison to Brook's last outing, Rabchenko's last fight was a second-round knockout of Siarhei Krapshyla in Borisov at the Palace of Culture.