UK light-heavyweight Joshua Buatsi made a winning yet unimpressive start to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a majority decision in a tight 10-round contest at the boxing arena.
But Parker had his moments, delivering effective individual punches in a fight where the approaches never quite clicked, with frequent clinching spoiling the contest.
The officials scored it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my best showing but how do champions respond? They succeed," Buatsi stated in the arena as he was faced boos from the spectators.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in February - to secure a twentieth professional win.
Several boxing experts felt the challenger, 31, merited the victory but the contender experienced the second setback of his 28-bout career.
The Champion Claims Victory in Uneventful Encounter
The fighter's advancement has stalled in recent years through management issues and extended periods of inactivity.
Earlier forecast as the future of British boxing, he now stands trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with neither fighter willing to overcommit in a tentative early stages.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after breaking his hand during the bout, was participating in his second appearance at light heavyweight.
By the middle rounds, Parker had stayed in contention, causing problems for the favorite, who utilized a tight guard to edge the better periods.
The crowd's patience decreased amid regular grabbing, with the challenger going down various instances during grappling.
Parker ended stronger, but many rounds were hard to judge. Although, former world champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
The victor progresses, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - on this evidence - still appears challenging.
Hatton Memorial Fuels Manchester Derby Fight
In the co-main event, Arthur beat Bradley Rea by split-decision in a terrific all-Manchester contest to secure the European light heavyweight championship.
The venue became quiet for a extremely emotional tribute before the fight as ten bells tolled in honor of local hero Hatton, who succumbed 46 years old in last month.
It was the first major televised fight night in the urban center since Hatton's passing. As the final chime disappeared, the quiet transitioned to a shout of "only one Hatton".
The action inside the ropes reflected the emotion. The eventual winner was knocked down by a left hook flush on the face in the initial stage, rising shakily to his footing on the referee's count.
But the red-colored shorts of the fighter soon pressed ahead again. From the other corner, the opponent - in rival City blue - was injured quickly, significant bruising developing under his face as the fighters traded powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace seldom decreased over 12 rounds.
Arthur barely secured the verdict with judges scorecards of even score, close margin and wider gap, but both fighters were persistent and courageous, everything their hero Hatton represented.
