British light heavyweight Joshua Buatsi made a winning yet underwhelming start to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a close ten-round fight at the boxing arena.
But Parker landed significant shots, landing some telling single shots in a match where the techniques never quite clicked, with constant grabbing disrupting the contest.
The officials scored it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my greatest showing but what defines champions? They win," the victor said in the ring as he was faced disapproval from the audience.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in February - to secure a 20th pro success.
Some ringside observers felt the challenger, thirty-one, merited the victory but the contender endured the second defeat of his 28-bout professional journey.
Buatsi Claims Win in Uneventful Affair
The fighter's advancement has plateaued in recent times through contract problems and extended periods of inactivity.
Previously predicted as the future of British boxing, he now finds himself trying to realize his potential - possibly in what appears to be a ultimate opportunity - under recent support.
He began cautiously, with the two boxers willing to overcommit in a tentative opening few rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in 2022 after damaging his hand in the contest, was making just his second fight at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, causing problems for the favorite, who worked behind a tight guard to barely take the better stanzas.
The audience's tolerance wore thin because of regular grabbing, with Parker slipping to the canvas various instances during close exchanges.
Parker closed well, but several stanzas were difficult to score. Nevertheless, former world champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
The victor advances, but with the likes of hard hitter Benavidez, and Russian champion Bivol ruling the division, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Memorial Inspires Manchester Derby Fight
In the secondary fight, Arthur defeated Bradley Rea by divided decision in a terrific all-Manchester battle to capture the European light heavyweight championship.
The stadium became quiet for a deeply poignant homage ahead of the contest as 10 bells sounded in remembrance of Manchester's own Hatton, who succumbed 46 years old in last month.
It was the first major televised match card in the urban center since Hatton's passing. As the last bell faded, the quiet transitioned to a chant of "there's just one Hatton".
The competition within the ring matched the feeling. Arthur was floored by a significant blow flush on the jaw in the early round, standing uncertainly to his footing on the referee's count.
But the Manchester United-red equipment of Arthur soon came forward again. Across the ring, the opponent - in opposing blue - was marked up early, significant bruising forming under his eye as the duo traded hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with powerful upward punches as the pace hardly diminished over the full distance.
Arthur narrowly won the result with official scores of draw, narrow lead and clearer margin, but both fighters were determined and courageous, all the qualities their inspiration the legend embodied.
