Home favourite Williams hit the canvas in rounds one, two and four after a horror start to silence a passionate Motorpoint Arena crowd as Eubank Jr – not normally known for his power – provided a counter-jabbing clinic, before the Welshman produced a stirring comeback to take the bout to his fierce rival.
However, Eubank Jr remained composed and sealed another controversial knockdown with an uppercut – which Williams claimed was merely a push – in the penultimate round that left his opponent needing an unlikely last-gasp knockout, showboating his way to victory in a fight that certainly did not lack for aggression and bad blood.
The judges at ringside returned scorecards of 116-109, 116-108 and 117-109 as Eubank Jr claimed a unanimous decision win that should set the 32-year-old up for a big challenge later in 2022.
While the Brighton middleweight moves to 33-2, Williams is left to reflect on those costly early struggles as he suffered a second successive loss and fourth of his career after a previous pair of defeats to Liam Smith and that unsuccessful WBO title challenge against Demetrius Andrade last year.
On a stacked undercard in the Welsh capital, the self-proclaimed ‘Greatest Woman of All Time’ Claressa Shields shone on her UK debut against Ema Kozin.
Defending her WBA, WBC, IBF, and The Ring female middleweight titles against undefeated mandatory and WBF champion Ema Kozin of Slovenia after a two-fight stint in MMA, the two-time Olympic champion failed to find a stoppage but nonetheless delivered a supreme display of variety, power and sheer skill and won every round on every judges scorecard.
Shields then engaged in a predictable post-fight war of words with great rival Savannah Marshall – the only opponent ever to defeat her as an amateur or professional – at ringside as the duo build up to securing one of the biggest fights in the history of women’s boxing later this year.
Elsewhere, ultra-talented amateur Caroline Dubois put her Tokyo Olympic disappointment behind her by making a winning start to her professional career with a dominant win over Lithuania’s Vaida Masiokaite.
Wales’ Chris Jenkins outpointed ageing former unified light-welterweight world champion Julius Indongo and Shane Gill upset Steve Robinson in a battle of novice heavyweights.
On the early card, there were wins for one-time Tyson Fury opponent Otto Wallin and Chris Eubank Jr’s cousin Harlem as well as Samuel Antwi.