UK light-heavyweight Joshua Buatsi made a winning yet underwhelming start to his career 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 competitive 10-round bout at the Co-op Live Arena.
But the challenger had his moments, connecting with powerful individual punches in a contest where the approaches failed to mesh, with excessive holding spoiling the fight.
Two judges had it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my greatest showing but what do champions do? They win," the victor commented in the ringside as he was met by boos from the spectators.
The British fighter returned to winning ways after his first professional defeat - an epic battle with Callum Smith in February - to secure a 20th pro success.
Several boxing experts felt the challenger, 31, merited the victory but the contender endured the second defeat of his 28-match career.
Buatsi Earns Triumph in Uneventful Affair
The fighter's advancement has plateaued in recent times through management issues and extended periods of lack of fights.
Previously predicted as the future of British boxing, he now is positioned trying to fulfil that early promise - maybe in what appears to be a last chance - under recent support.
He began cautiously, with neither fighter ready to overcommit in a tentative early stages.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after damaging his hand in the contest, was competing in only his second fight at the higher weight class.
By the middle rounds, Parker had stayed in contention, causing problems for the favorite, who operated with a tight guard to barely take the cleaner periods.
The audience's tolerance diminished amid regular grabbing, with the challenger slipping to the canvas multiple occasions during close exchanges.
Parker closed well, but many rounds were challenging to assess. Nevertheless, former world champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for the challenger, giving Buatsi just one round.
The victor advances, but with the presence of heavy hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Homage Inspires All-Manchester Battle
In the co-main event, Arthur overcame Rea by close verdict in a terrific all-Manchester battle to capture the European light heavyweight title.
The arena grew hushed for a deeply poignant homage ahead of the contest as ten bells tolled in memory of the city's native Hatton, who died 46 years old in last month.
It was the initial significant broadcast fight night in the location since Hatton's death. As the concluding sound disappeared, the stillness became a shout of "only one Ricky Hatton".
The action during the bout equaled the feeling. Arthur was sent to the canvas by a significant blow flush on the face in the early round, rising shakily to his footing on the referee's count.
But the red-colored attire of Arthur soon came forward again. On the opposite side, Rea - in rival City blue - was injured quickly, significant bruising developing under his face as the fighters exchanged hard punches.
Rea, 27, delivered effective strikes but the champion, 34, responded in kind with powerful upward punches as the intensity seldom decreased over twelve rounds.
The victor barely secured the decision with scoring tallies of 114-114, 115-113 and wider gap, but both fighters were determined and brave, exactly what their inspiration Hatton embodied.
