British light-heavyweight Joshua Buatsi secured a victory yet unimpressive debut to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a close ten-round bout at the boxing arena.
But Parker found success, landing some telling individual punches in a fight where the techniques didn't complement each other, with excessive holding marring the contest.
The scoring judges judged it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my finest display but what do champions do? They succeed," Buatsi commented in the ring as he was met by boos from the audience.
The Londoner bounced back after his maiden career setback - an memorable fight with Callum Smith in February - to earn a 20th career victory.
Various analysts thought the challenger, 31, deserved the victory but the British boxer endured the second defeat of his 28-fight professional journey.
Buatsi Secures Victory in Uneventful Match
The fighter's advancement has stalled in recent years through contract problems and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now finds himself trying to fulfil that early promise - perhaps in what appears to be a last chance - under fresh management.
He started carefully, with the two boxers ready to overcommit in a tentative initial rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in 2022 after suffering a hand injury in the contest, was participating in his second appearance at light-heavyweight.
By the fight's midpoint, the underdog had stayed in contention, causing problems for the favorite, who operated with a solid defense to narrowly win the better periods.
The spectators' acceptance decreased because of constant clinching, with the challenger slipping to the canvas multiple occasions during close exchanges.
Parker finished the stronger, but many rounds were hard to judge. Nevertheless, ex-champion Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
Buatsi advances, but with the caliber of hard hitter David Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Tribute Inspires Manchester Derby Battle
In the secondary fight, Arthur beat Rea by close verdict in a excellent Manchester vs Manchester contest to win the European light heavyweight championship.
The stadium grew hushed for a extremely emotional homage prior to the bout as ten bells rang in memory of local hero Hatton, who succumbed at age 46 in September.
It was the first major televised fight night in the location since Hatton's passing. As the final chime ended, the stillness gave way to a shout of "there's only one Ricky Hatton".
The action within the ring matched the emotion. Arthur was knocked down by a significant blow directly to the jaw in the initial stage, rising shakily to his feet on the referee's count.
But the Manchester United-red attire of the fighter soon advanced again. From the other corner, Rea - in competitive blue - was marked up quickly, significant bruising appearing under his orbital area as the duo landed punishing blows.
The challenger, 27, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the intensity seldom decreased over twelve rounds.
The victor edged the result with judges scorecards of 114-114, close margin and 115-112, but each competitor were relentless and courageous, all the qualities their idol Hatton embodied.
