UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming beginning to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a judges' verdict in a close 10-round fight at the boxing arena.
But Parker landed significant shots, landing some telling individual punches in a match where the techniques failed to mesh, with constant grabbing disrupting the action.
Two judges had it 96-94 in favor to the winner, with the third a 95-95 draw.
"It wasn't my greatest display but what defines champions? They win," Buatsi stated in the arena as he was faced negative reactions from the crowd.
The British fighter got back to winning after his first professional defeat - an epic battle with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers thought the challenger, thirty-one, should have been awarded the decision but the contender suffered the second loss of his 28-match professional journey.
Buatsi Claims Win in Slow Encounter
The fighter's advancement has plateaued in recent times through management issues and considerable time of lack of fights.
Previously predicted as the next star of UK boxing, he now is positioned trying to fulfil that early promise - perhaps in what appears to be a last chance - under recent support.
He opened tentatively, with both competitors prepared to overcommit in a cagey opening few rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after damaging his hand in the contest, was making just his second appearance at light-heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who operated with a protective stance to edge the more effective stanzas.
The spectators' acceptance decreased amid constant clinching, with the challenger going down multiple occasions during clinches.
The underdog ended stronger, but multiple periods were hard to judge. Although, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
The victor moves on, but with the caliber of hard hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - judging by this showing - still appears challenging.
Hatton Tribute Fuels Manchester Derby Battle
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a excellent all-Manchester fight to secure the European light heavyweight belt.
The arena became quiet for a profoundly moving tribute ahead of the contest as a bell ceremony sounded in honor of Manchester's own Hatton, who died at age 46 in recently.
It was the first major televised match card in the location since Hatton's passing. As the last bell ended, the quiet transitioned to a chant of "there's only one Ricky Hatton".
The competition during the bout matched the feeling. Arthur was sent to the canvas by a significant blow squarely on the face in the early round, getting up unsteadily to his footing on the referee's count.
But the Manchester United-red shorts of the fighter soon advanced again. Across the ring, the opponent - in rival City blue - was marked up early, noticeable damage forming under his orbital area as the pair exchanged hard punches.
The challenger, 27, landed power punches but the champion, 34, matched the intensity with powerful upward punches as the pace hardly diminished over twelve rounds.
Arthur barely secured the decision with official scores of draw, close margin and wider gap, but both fighters were persistent and brave, everything their hero Hatton stood for.
