British light-heavyweight Joshua Buatsi earned a win yet underwhelming debut to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a split decision in a competitive 10-round contest at the boxing arena.
But Parker found success, delivering effective clean blows in a contest where the techniques failed to mesh, with frequent clinching spoiling the action.
Two judges judged it 96-94 to the winner, with the remaining official a even score.
"It wasn't my finest display but what do champions do? They win," Buatsi said in the arena as he was greeted with boos from the crowd.
The British fighter got back to winning after his first professional defeat - an thrilling contest with Callum Smith in February - to secure a twentieth professional win.
Various analysts thought the challenger, thirty-one, deserved the win but the Derbyshire fighter suffered the second setback of his 28-bout professional journey.
Buatsi Secures Victory in Uneventful Affair
Buatsi's progress has stalled in recent times through management issues and long spells of lack of fights.
Previously predicted as the next star of the British fight scene, he now is positioned trying to fulfil that early promise - perhaps in what feels like a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers prepared to overcommit in a tentative initial rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was competing in only his second appearance at light heavyweight.
By the middle rounds, Parker had stayed in contention, making life awkward for the favorite, who worked behind a tight guard to narrowly win the more effective stanzas.
The spectators' acceptance wore thin during constant clinching, with Parker slipping to the canvas multiple occasions during clinches.
Parker finished the stronger, but several stanzas were challenging to assess. Nevertheless, former world champion Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, giving Buatsi just one round.
Buatsi progresses, but with the presence of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - on this evidence - still looks steep.
Hatton Tribute Fuels Manchester Derby Fight
In the co-main event, Arthur beat Rea by divided decision in a excellent local rivalry battle to win the European light heavyweight title.
The venue fell silent for a extremely emotional homage before the fight as ten bells rang in honor of Manchester's own Ricky Hatton, who passed away 46 years old in September.
It was the first major televised fight night in the urban center since Hatton's death. As the final chime ended, the quiet gave way to a shout of "there's just one Hatton".
The competition during the bout equaled the sentiment. Arthur was knocked down by a left hook directly to the chin in the initial stage, getting up unsteadily to his footing on the referee's count.
But the red-colored attire of the fighter soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was marked up early, noticeable damage developing under his eye as the pair traded punishing blows.
Rea, 27, connected with strong blows but Arthur, 34, fought fire with fire with stinging uppercuts as the intensity seldom decreased over 12 rounds.
Arthur barely secured the decision with scoring tallies of 114-114, close margin and wider gap, but both fighters were relentless and brave, all the qualities their inspiration Hatton represented.
