British light-heavyweight Joshua Buatsi made a winning yet underwhelming beginning to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a tight 10-round contest at the Manchester venue.
But the challenger found success, landing some telling clean blows in a contest where the styles failed to mesh, with frequent clinching disrupting the contest.
Two judges judged it 96-94 to the winner, with the remaining official a even score.
"It wasn't my greatest display but how do champions respond? They win," Buatsi said in the arena as he was greeted with disapproval from the spectators.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Some ringside observers believed Parker, thirty-one, merited the decision but the Derbyshire fighter experienced the second defeat of his 28-bout professional journey.
The Champion Secures Victory in Uneventful Match
The fighter's advancement has slowed in recent years through promotional disputes and long spells of inactivity.
Previously predicted as the rising talent of the British fight scene, he now stands trying to achieve expectations - perhaps in what feels like a ultimate opportunity - under recent support.
He opened tentatively, with neither fighter prepared to take risks in a calculated early stages.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was making just his second bout at the higher weight class.
By the middle rounds, the underdog had made it competitive, making life awkward for the favorite, who utilized a protective stance to barely take the cleaner rounds.
The audience's tolerance wore thin during regular grabbing, with the challenger slipping to the canvas several times during clinches.
The underdog closed well, but many rounds were challenging to assess. Nevertheless, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the likes of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Hatton Memorial Motivates Manchester Derby Contest
In the supporting bout, Arthur defeated Rea by close verdict in a outstanding Manchester vs Manchester fight to secure the European light-heavyweight belt.
The venue grew hushed for a deeply poignant memorial prior to the bout as a bell ceremony rang in remembrance of the city's native Hatton, who passed away at age 46 in last month.
It was the first major televised fight night in the city since the passing of Hatton. As the last bell ended, the silence transitioned to a roar of "there's only one Hatton".
The competition within the ring matched the sentiment. The eventual winner was sent to the canvas by a significant blow directly to the chin in the early round, standing uncertainly to his footing on the eight count.
But the Manchester United-red attire of Arthur soon pressed ahead again. Across the ring, the opponent - in rival City blue - was damaged quickly, noticeable damage appearing under his eye as the fighters exchanged hard punches.
Rea, 27, connected with strong blows but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the intensity rarely dropped over twelve rounds.
The victor barely secured the decision with judges scorecards of even score, narrow lead and clearer margin, but the two athletes were relentless and courageous, all the qualities their hero the legend embodied.
