UK light-heavyweight Joshua Buatsi made a winning yet unimpressive start to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a close 10-round contest at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling individual punches in a match where the approaches never quite clicked, with constant grabbing spoiling the action.
Two judges judged it 96-94 to Buatsi, with the third a even score.
"It wasn't my finest display but how do champions respond? They succeed," the victor stated in the ringside as he was met by boos from the crowd.
The Londoner bounced back after his initial pro loss - an memorable fight with Callum Smith in February - to secure a twentieth professional win.
Several boxing experts believed Parker, thirty-one, should have been awarded the decision but the Derbyshire fighter endured the second loss of his 28-fight professional journey.
The Champion Claims Victory in Dull Encounter
The fighter's advancement has stalled in the past few years through promotional disputes and long spells of inactivity.
Previously predicted as the next star of UK boxing, he now is positioned trying to fulfil that early promise - maybe in what seems like a final roll of the dice - under fresh management.
He began cautiously, with neither fighter willing to take risks in a tentative opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in 2022 after suffering a hand injury in the contest, was making just his second appearance at light heavyweight.
By the middle rounds, the underdog had kept it close, making life awkward for Buatsi, who utilized a solid defense to narrowly win the better stanzas.
The crowd's patience decreased amid regular grabbing, with the challenger slipping to the canvas various instances during close exchanges.
The underdog finished the stronger, but several stanzas were hard to judge. However, ex-champion the boxing analyst - commentating on Dazn - had it particularly wide for the challenger, scoring for Buatsi just a single round.
Buatsi progresses, but with the presence of power puncher David Benavidez, and Russian star Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Hatton Homage Inspires All-Manchester Contest
In the secondary fight, Arthur beat Bradley Rea by split-decision in a outstanding all-Manchester contest to secure the continental title.
The arena grew hushed for a deeply poignant tribute prior to the bout as 10 bells sounded in honor of local hero Hatton, who succumbed 46 years old in recently.
It was the premier televised boxing event in the city since Hatton's passing. As the last bell faded, the silence transitioned to a roar of "there's just one Hatton".
The fighting inside the ropes reflected the feeling. The eventual winner was sent to the canvas by a significant blow flush on the chin in the early round, rising shakily to his footing on the eight count.
But the traditional red equipment of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was damaged early, noticeable damage developing under his orbital area as the fighters traded powerful shots.
Rea, 27, delivered effective strikes but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the action rarely dropped over 12 rounds.
The victor narrowly won the result with judges scorecards of even score, close margin and 115-112, but each competitor were persistent and brave, all the qualities their hero Hatton embodied.
