UK light heavyweight Joshua Buatsi made a winning yet unimpressive start to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a competitive ten-round fight at the Manchester venue.
But the challenger had his moments, connecting with powerful clean blows in a contest where the approaches didn't complement each other, with frequent clinching disrupting the action.
The officials judged it 96-94 in favor to the winner, with the third a 95-95 draw.
"It wasn't my finest display but what do champions do? They win," Buatsi commented in the ringside as he was faced disapproval from the spectators.
The Londoner returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in February - to claim a twentieth professional win.
Some ringside observers thought Parker, thirty-one, deserved the decision but the Derbyshire fighter experienced the second defeat of his 28-bout career.
The Champion Claims Victory in Uneventful Encounter
His career development has stalled in recent years through management issues and considerable time of inactivity.
Earlier forecast as the future of the British fight scene, he now finds himself trying to realize his potential - possibly in what feels like a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers ready to overcommit in a calculated initial rounds.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in 2022 after suffering a hand injury mid-fight, was making just his second appearance at the higher weight class.
By the fight's midpoint, the underdog had kept it close, making life awkward for Buatsi, who worked behind a solid defense to barely take the more effective periods.
The spectators' acceptance decreased because of frequent holding, with Parker falling to the floor several times during grappling.
The underdog finished the stronger, but several stanzas were hard to judge. Although, former world champion Carl Frampton - providing analysis for Dazn - had it particularly wide for Parker, awarding Buatsi just only one stanza.
The victor progresses, but with the caliber of power puncher David Benavidez, and Russian star Bivol leading the category, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Memorial Fuels Manchester Derby Fight
In the supporting bout, Arthur beat Rea by split-decision in a excellent all-Manchester contest to capture the European light-heavyweight title.
The arena became quiet for a profoundly moving tribute ahead of the contest as a bell ceremony sounded in memory of Manchester's own Hatton, who died 46 years old in recently.
It was the initial significant broadcast match card in the city since Hatton's passing. As the final chime faded, the quiet became a shout of "there's only one Hatton".
The fighting inside the ropes equaled the emotion. The eventual winner was sent to the canvas by a significant blow flush on the chin in the initial stage, getting up unsteadily to his footing on the referee's count.
But the red-colored attire of Arthur soon advanced again. Across the ring, Rea - in opposing blue - was damaged soon, noticeable damage developing under his face as the duo exchanged punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, matched the intensity with stinging uppercuts as the action rarely dropped over 12 rounds.
The victor edged the result with judges scorecards of even score, 115-113 and clearer margin, but each competitor were relentless and brave, everything their inspiration the legend stood for.
