British light heavyweight Joshua Buatsi made a winning yet underwhelming debut to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a tight 10-round bout at the Co-op Live Arena.
But the challenger found success, landing some telling single shots in a fight where the techniques never quite clicked, with frequent clinching marring the action.
Two judges scored it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my finest performance but what defines champions? They win," Buatsi commented in the arena as he was greeted with negative reactions from the crowd.
The British fighter got back to winning after his maiden career setback - an epic battle with his previous opponent in last winter - to claim a 20th career victory.
Some ringside observers felt Parker, 31, merited the victory but the Derbyshire fighter endured the second defeat of his 28-fight professional journey.
Buatsi Claims Win in Uneventful Match
Buatsi's progress has slowed in recent times through management issues and extended periods of inactivity.
Once tipped as the future of British boxing, he now finds himself trying to fulfil that early promise - perhaps in what feels like a final roll of the dice - under fresh management.
He opened tentatively, with neither fighter ready to take risks in a calculated early stages.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was making just his second bout at the higher weight class.
By the halfway stage, the underdog had made it competitive, creating difficulties for the favorite, who operated with a protective stance to barely take the more effective periods.
The audience's tolerance decreased amid frequent holding, with Parker going down multiple occasions during grappling.
The underdog finished the stronger, but multiple periods were challenging to assess. Nevertheless, ex-champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for Parker, giving Buatsi just only one stanza.
The victor advances, but with the caliber of power puncher David Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Hatton Homage Fuels All-Manchester Fight
In the supporting bout, Arthur beat Bradley Rea by close verdict in a terrific local rivalry contest to secure the European light heavyweight title.
The arena grew hushed for a deeply poignant homage prior to the bout as ten bells tolled in memory of Manchester's own Ricky Hatton, who passed away 46 years old in September.
It was the initial significant broadcast fight night in the city since Hatton's passing. As the last bell faded, the quiet became a roar of "there's only one Hatton".
The fighting during the bout reflected the feeling. The eventual winner was sent to the canvas by a left hook flush on the face in the early round, getting up unsteadily to his feet on the eight count.
But the traditional red shorts of Arthur soon came forward again. On the opposite side, Rea - in competitive blue - was injured soon, significant bruising forming under his eye as the pair exchanged powerful shots.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with stinging uppercuts as the action rarely dropped over 12 rounds.
Arthur edged the result with official scores of even score, close margin and 115-112, but both fighters were determined and full of heart, exactly what their inspiration Hatton embodied.
