British light heavyweight Joshua Buatsi secured a victory yet disappointing debut to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a close ten-round fight at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful clean blows in a match where the approaches failed to mesh, with frequent clinching marring the fight.
The officials judged it 96-94 for to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest display but what defines champions? They win," the victor commented in the ring as he was faced disapproval from the spectators.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in last winter - to claim a 20th career victory.
Some ringside observers thought the challenger, 31, should have been awarded the win but the contender suffered the second setback of his 28-bout career.
Buatsi Secures Win in Dull Encounter
His career development has plateaued in recent years through contract problems and considerable time of lack of fights.
Previously predicted as the future of British boxing, he now is positioned trying to achieve expectations - maybe in what feels like a final roll of the dice - under fresh management.
He started carefully, with both competitors willing to take risks in a cagey opening few rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in 2022 after suffering a hand injury mid-fight, was making just his second bout at light heavyweight.
By the fight's midpoint, the underdog had kept it close, causing problems for Buatsi, who operated with a protective stance to barely take the cleaner periods.
The spectators' acceptance decreased because of constant clinching, with the challenger going down several times during close exchanges.
Parker ended stronger, but multiple periods were hard to judge. Nevertheless, former world champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, giving Buatsi just a single round.
Buatsi moves on, but with the likes of power puncher David Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Tribute Motivates Manchester Derby Battle
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a excellent local rivalry battle to secure the European light heavyweight belt.
The stadium fell silent for a profoundly moving homage ahead of the contest as ten bells rang in remembrance of the city's native Ricky Hatton, who passed away 46 years old in recently.
It was the premier televised boxing event in the urban center since Hatton's passing. As the concluding sound ended, the stillness gave way to a shout of "only one Hatton".
The competition within the ring matched the feeling. The eventual winner was floored by a powerful punch flush on the chin in the early round, getting up unsteadily to his footing on the eight count.
But the traditional red equipment of the fighter soon advanced again. From the other corner, the opponent - in rival City blue - was injured quickly, noticeable damage developing under his eye as the pair exchanged punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, matched the intensity with effective uppercuts as the intensity rarely dropped over 12 rounds.
Arthur edged the result with official scores of draw, 115-113 and clearer margin, but the two athletes were persistent and courageous, all the qualities their hero Hatton represented.
