British light heavyweight Joshua Buatsi made a winning yet underwhelming beginning to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a split decision in a close ten-round bout at the Manchester venue.
But the challenger found success, connecting with powerful single shots in a contest where the techniques never quite clicked, with constant grabbing marring the action.
The officials scored it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my greatest display but how do champions respond? They win," the victor commented in the arena as he was met by negative reactions from the audience.
The British fighter got back to winning after his first professional defeat - an thrilling contest with Callum Smith in February - to claim a 20th pro success.
Several boxing experts felt Parker, 31, merited the decision but the Derbyshire fighter suffered the second loss of his 28-match career.
Buatsi Earns Victory 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 the British fight scene, he now finds himself trying to fulfil that early promise - possibly in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with both competitors willing to take risks in a cagey early stages.
Parker, whose sole prior loss came at the lower weight class against John Ryder in 2022 after suffering a hand injury during the bout, was participating in his second appearance at the higher weight class.
By the halfway stage, the underdog had made it competitive, creating difficulties for Buatsi, who operated with a tight guard to narrowly win the cleaner periods.
The crowd's patience decreased amid frequent holding, with Parker falling to the floor various instances during clinches.
Parker closed well, but several stanzas were hard to judge. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, scoring for Buatsi just one round.
The victor advances, but with the caliber of hard hitter David Benavidez, and Russian champion Bivol ruling the division, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Homage Inspires Manchester Derby Fight
In the supporting bout, Lyndon Arthur overcame Rea by divided decision in a excellent all-Manchester fight to secure the continental title.
The stadium fell silent for a deeply poignant memorial prior to the bout as ten bells tolled in memory of Manchester's own Hatton, who succumbed at age 46 in September.
It was the initial significant broadcast match card in the location since Hatton's passing. As the concluding sound faded, the silence transitioned to a roar of "there's only one Ricky Hatton".
The fighting within the ring equaled the feeling. Arthur was sent to the canvas by a left hook directly to the jaw in the initial stage, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red attire of the fighter soon advanced again. On the opposite side, Rea - in opposing blue - was injured quickly, noticeable damage appearing under his orbital area as the pair landed hard punches.
Rea, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with effective uppercuts as the intensity hardly diminished over the full distance.
The victor barely secured the result with official scores of even score, 115-113 and clearer margin, but both fighters were determined and courageous, everything their inspiration Hatton represented.
