UK light heavyweight Joshua Buatsi earned a win yet disappointing beginning to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a competitive ten-round contest at the Manchester venue.
But Parker had his moments, landing some telling individual punches in a fight where the styles failed to mesh, with constant grabbing spoiling the fight.
The scoring judges scored it 96-94 in favor to the winner, with the third a even score.
"It wasn't my finest display but what do champions do? They prevail," the victor stated in the arena as he was faced negative reactions from the crowd.
The Londoner returned to winning ways after his initial pro loss - an epic battle with Callum Smith in last winter - to earn a twentieth professional win.
Several boxing experts felt Parker, 31, deserved the win but the contender suffered the second defeat of his 28-fight career.
The Champion Secures Triumph in Uneventful Match
His career development has slowed in recent years through promotional disputes and extended periods of inactivity.
Once tipped as the rising talent of UK boxing, he now is positioned trying to realize his potential - possibly in what feels like a ultimate opportunity - under recent support.
He opened tentatively, with both competitors ready to take risks in a tentative initial rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in 2022 after damaging his hand mid-fight, was competing in only his second bout at the higher weight class.
By the fight's midpoint, the underdog had kept it close, causing problems for the favorite, who utilized a solid defense to barely take the cleaner stanzas.
The crowd's patience wore thin amid frequent holding, with the challenger falling to the floor multiple occasions during grappling.
The underdog finished the stronger, but several stanzas were challenging to assess. Although, former world champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for Parker, awarding Buatsi just a single round.
Buatsi moves on, but with the presence of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - on this evidence - still seems difficult.
Hatton Tribute Motivates Manchester Derby Battle
In the co-main event, Arthur defeated Rea by divided decision in a terrific all-Manchester battle to secure the European light-heavyweight belt.
The venue became quiet for a profoundly moving homage ahead of the contest as 10 bells sounded in remembrance of Manchester's own Hatton, who succumbed aged 46 in September.
It was the initial significant broadcast match card in the urban center since Hatton's passing. As the concluding sound ended, the stillness transitioned to a shout of "there's only one Hatton".
The action during the bout equaled the sentiment. The eventual winner was sent to the canvas by a left hook flush on the face in the second round, standing uncertainly to his footing on the count of eight.
But the red-colored shorts of the fighter soon pressed ahead again. Across the ring, the opponent - in opposing blue - was injured quickly, heavy swelling developing under his orbital area as the fighters landed powerful shots.
The challenger, 27, connected with strong blows but Arthur, thirty-four, responded in kind with powerful upward punches as the pace seldom decreased over 12 rounds.
Arthur narrowly won the verdict with judges scorecards of even score, close margin and 115-112, but each competitor were relentless and courageous, everything their hero Hatton represented.
