British light heavyweight Joshua Buatsi earned a win yet disappointing debut to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a tight 10-round fight at the Manchester venue.
But the challenger landed significant shots, landing some telling clean blows in a fight where the approaches failed to mesh, with excessive holding disrupting the contest.
Two judges had it 96-94 to the winner, with the remaining official a even score.
"It wasn't my best performance but what do champions do? They win," the victor commented in the arena as he was greeted with boos from the spectators.
The Londoner got back to winning after his maiden career setback - an epic battle with Callum Smith in last winter - to claim a twentieth professional win.
Some ringside observers thought the challenger, thirty-one, should have been awarded the win but the British boxer experienced the second setback of his 28-fight career.
Buatsi Earns Triumph in Uneventful Affair
Buatsi's progress has stalled in recent times through contract problems and considerable time of inactivity.
Earlier forecast as the rising talent of UK boxing, he now is positioned trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers willing to overcommit in a calculated initial rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in 2022 after breaking his hand mid-fight, was competing in only his second bout at the higher weight class.
By the fight's midpoint, the underdog had kept it close, causing problems for the favorite, who worked behind a protective stance to barely take the cleaner periods.
The crowd's patience wore thin during frequent holding, with the challenger falling to the floor multiple occasions during close exchanges.
The underdog closed well, but several stanzas were difficult to score. Although, previous titleholder Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, giving Buatsi just one round.
The victor moves on, but with the likes of heavy hitter David Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - based on this performance - still seems difficult.
Hatton Tribute Fuels All-Manchester Fight
In the co-main event, Arthur defeated Rea by divided decision in a excellent Manchester vs Manchester battle to secure the European light heavyweight belt.
The stadium became quiet for a deeply poignant tribute prior to the bout as 10 bells sounded in memory of the city's native Ricky Hatton, who passed away 46 years old in September.
It was the premier televised boxing event in the urban center since Hatton's passing. As the last bell disappeared, the stillness became a chant of "there's only one Ricky Hatton".
The action during the bout reflected the feeling. The eventual winner was sent to the canvas by a significant blow squarely on the chin in the initial stage, getting up unsteadily to his footing on the count of eight.
But the red-colored attire of Arthur soon came forward again. On the opposite side, the opponent - in competitive blue - was marked up early, significant bruising developing under his face as the fighters exchanged powerful shots.
Rea, twenty-seven, landed power punches but Arthur, 34, responded in kind with effective uppercuts as the intensity seldom decreased over 12 rounds.
The victor edged the verdict with scoring tallies of 114-114, narrow lead and wider gap, but the two athletes were determined and courageous, all the qualities their idol Hatton embodied.
