George Groves finished a wild night in Manchester with his left arm hanging redundantly by his side, his WBA super-middleweight title intact, a cheque for £1.6m safely lodged and the prospect of more to come in the final of the World Boxing Super Series in London on 2 June.

Chris Eubank Jr, cruelly, went home to Brighton with nothing but a significant blood deficit from gaping cuts across his features and the acknowledgment of a capacity crowd whose jeers turned to cheers after his full-throttle effort to blow the Londoner out of the ring over 12 rounds. It was little comfort, although they might do it all again once this tournament is over. Groves now awaits the winner of next weekend’s semi-final in Nuremberg between the unbeaten Liverpudlian Callum Smith and Jürgen Brähmer.

George Groves beats Chris Eubank Jr: World Boxing Super Series - as it happened Read more

Groves’s most immediate challenge is to fix his shoulder. “I dislocated it in the last round,” he said ringside, paying Eubank, the IBO champion, due homage for a spirited fight. Eubank, naturally, disagreed firmly with the verdict.

From this vantage point at ringside, the first semi-final was closer than two of the three judges reckoned. Howard Foster scored it 117-112 and Steve Gray had 116-112, both for the winner, while Marcus McDonnell’s card of 115-113 for Groves was closer to many estimates. The Observer gave Eubank six rounds, Groves five, with one even, or 115-114 in favour of the Brighton fighter.

Eubank sashayed to the ring; Groves did his London geezer walk. They stayed true to their chosen cliches – but not for long. As with so many fights overloaded with emotion, the drama and the action cascaded into the final moments. It was an uneven, scrappy contest, but memorable nonetheless.

Groves, crouching with feet spread wide to launch his shots from distance, circled his opponent, who lunged and grabbed to get under long leads, but struggled to avoid the bigger man’s chopping rights. As he had done in a slow start against Billy Joe Saunders in 2014, Eubank had to take a lecture from his father between rounds to up his workrate. He duly did and emerged from one wild melee with blood leaking from the upper corner of his right eye. Groves now had a target; Eubank had a claret-soaked problem.

Distracted by his wound, Eubank struggled to shrug off the look of a put-upon underdog. The difference in size – Groves will have outweighed him by nearly a stone since loading up after the weigh-in – had played some part in the tactics of both fighters, but Eubank did enough in the fourth to get on the scorecard.

After a quarter of an hour of untidy jousting, the contest clicked into life. Adrenalin had replaced the early anxiety and the punches flowed – as did the blood from Eubank’s eye. Still, he outworked his man to post another round in his favour. Eubank now played a dangerous game, swinging without care from all angles, leaving himself open to counters, but choosing to ratchet up the physicality. It won him the sixth.

The smaller man was not the weaker – far from it – and he swarmed over Groves at every opportunity, but he was gambling with borrowed chips. Every ill-judged swipe had a potential price attached. Groves, who was not throwing enough punches to catch the judges’ attention, needed to stop the charge of his bleeding foe, but found him awkward, stubborn and fearless. The Londoner had the single-shot menace to do damage, but his radar was off – until a flurry had Eubank in trouble for the first time in his career towards the end of the eighth, Groves’s first round in more than 12 minutes.

Was this a momentum swing or a blip? Eubank was determined to prove it was the latter, as he stormed into the WBA champion. He does not lack for courage or self-belief, and a couple of stout headshots won him the ninth. Groves was getting caught by telegraphed shots – not a good sign with nine minutes left – but Eubank was catching plenty too as boxing surrendered to brawling.

It would not be a quiet finish. Eubank, now cut deeply across his eye and nose, gave Groves little room to do his work, but was hammered for his pains in the 11th. They touched gloves at the start of the final three minutes, but the contact thereafter was far from friendly, Eubank lashing madly to not much effect.

George Groves and Chris Eubank Jr trade verbal blows before showdown Read more

And then came the most dramatic finish to a fight in a British ring for a long while. Groves, his left arm dangling uselessly by his side, was battered from one side of the ring to the other, but somehow stayed upright, and threw what counters he could with his right.

Sharp-eyed devotees among the 20,000 fans who came from London, Brighton and all parts north will have noticed two interesting fights on the undercard.

Sebastian Eubank, Junior’s brother, made his professional debut, and looked solid in outpointing Polish cruiser Kamil Kulcczyk over four rounds. He joins a clan of several who have boxed as a Eubank (although the family name is Eubanks).

When Derbyshire super-middleweight prospect Zach Parker stretched his unbeaten run to 15 by stopping the 31-year-old Spaniard Adasat Rodriguez in the second of 10 rounds, his 11th inside the distance, Chris Eubank Sr surely will have recognised some of the winner’s moves. Zach’s father, Darren, a light-middleweight, entertained el gran senor of the Eubank family on his British debut after his brief American sojourn, losing to the monocled one in the first round of six, 30 years ago almost to the day.

In bouts of less quirky history but more title clout, Tommy Langford kept his British middleweight belt with a hard-fought points win over Jack Arnfield; while Ryan Walsh, super-fit (he rarely sits between rounds) and applying educated pressure throughout, had to settle for a draw against the noticeably bigger Isaac Lowe, a decision which incensed his brother, Michael, but it was enough for him to remain British featherweight champion.